What Is The Basic Structure Of Human Hair And Nails

The structure of people's hair

Fei-Chi Yang

Section of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada

Yuchen Zhang

Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada

Maikel C. Rheinstädter

Section of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada

Bookish Editor: Mikko Karttunen

Received 2014 Aug seven; Accepted 2014 Sep 22.

Supplementary Materials: Supplemental Information one: Two-dimensional X-ray Data of All 12 Subjects Two-dimensional X-ray data of all 12 subjects investigated in this study. Data are provided as 2-dimensional matrices in Matlab format ('subject1.mat'). The file 'PeerJ_load_data.grand' is a Matlab macro to load and visualize the 2-dimensional data sets.

DOI:10.7717/peerj.619/supp-1

Abstruse

Hair is a filamentous biomaterial consisting mainly of proteins in particular keratin. The structure of human hair is well known: the medulla is a loosely packed, disordered region most the middle of the hair surrounded by the cortex, which contains the major part of the fibre mass, mainly consisting of keratin proteins and structural lipids. The cortex is surrounded by the cuticle, a layer of dead, overlapping cells forming a protective layer around the pilus. The respective structures have been studied extensively using a variety of different techniques, such as lite, electron and atomic forcefulness microscopes, and also X-ray diffraction. We were interested in the question how much the molecular pilus structure differs from person to person, between male person and female pilus, hair of different appearances such every bit colour and waviness. We included hair from parent and child, identical and fraternal twins in the study to come across if genetically similar pilus would show similar structural features.

The molecular structure of the pilus samples was studied using high-resolution Ten-ray diffraction, which covers length scales from molecules upwards to the system of secondary structures. Signals due to the coiled-coil phase of α-helical keratin proteins, intermediate keratin filaments in the cortex and from the lipid layers in the cell membrane circuitous were observed in the specimen of all individuals, with very small deviations. Despite the relatively small number of individuals (12) included in this study, some conclusions tin can exist drawn. While the general features were observed in all individuals and the corresponding molecular structures were virtually identical, additional signals were observed in some specimen and assigned to different types of lipids in the cell membrane complex. Genetics seem to play a role in this composition as identical patterns were observed in pilus from male parent and girl and identical twins, however, not for fraternal twins. Identification and characterization of these features is an of import step towards the detection of abnormalities in the molecular structure of pilus every bit a potential diagnostic tool for sure diseases.

Keywords: Human hair, Molecular construction, Ten-ray diffraction, Keratin, Intermediate filament, Coiled-coil proteins, Alpha helix, Cell membrane complex

Introduction

Human scalp hair is a bio-synthesized cloth that has a complex internal construction. The adult human pilus is effectually twenty–180 µm in width, and mostly grows to a length of approximately 90 cm. Information technology consists of many layers including the cuticle, the cortex and the medulla. These layers are bound together by the prison cell membrane complex (Robbins, 2012).

The construction of man hair is well known and in particular X-ray diffraction revealed details of molecular structure and organization within hair (Fraser et al., 1986; Briki et al., 2000; Busson, Engstrom & Doucet, 1999; Randebrook, 1964; Fraser, MacRae & Rogers, 1962; Kreplak et al., 2001b; Wilk, James & Amemiya, 1995; Pauling & Corey, 1951; Ohta et al., 2005; Astbury & Street, 1932; Astbury & Forest, 1934; Astbury & Sisson, 1935; Franbourg et al., 2003; Rafik, Doucet & Briki, 2004; James et al., 1999; Veronica & Amemiya, 1998; Briki et al., 1999; James, 2001). In item microbeam small angle X-ray scattering techniques enables the determination of hair structure with a loftier spatial resolution (Iida & Noma, 1993; Busson, Engstrom & Doucet, 1999; Kreplak et al., 2001b; Ohta et al., 2005; Kajiura et al., 2006). Information technology is a long-standing question whether changes in the molecular structure of blast or pilus tin exist related to certain diseases and potentially be used equally a diagnostic tool. Such a technique would in item exist interesting and relevant every bit simple, non-invasive screening method for cancer (James et al., 1999; Briki et al., 1999; James, 2001). Abnormal kinky hair is, for instance, feature of giant axonal neuropathy (Berg, Rosenberg & Asbury, 1972).

The purpose of this report is to apply X-ray diffraction to clarify the construction of human scalp pilus for individuals with differing characteristics. The 12 individuals in this study include hair from men and women and hair of different colour and appearance, such as direct, wavy and curly. In addition to appearance, the study also includes pilus from a male parent and daughter, a pair of identical and a pair of fraternal twins to include genetic similarities. All hair was collected from healthy individuals and care was taken that the hair was not permed or dyed before the experiments.

Signals due to the coiled-coil organization of α-helical keratin proteins and intermediate filaments in the cortex, and lipids in the cell membrane complex were observed in the hair of all individuals. While these general features occur independent of gender or appearance of the hair with a very small standard deviation in the underlying molecular dimensions, we find significant differences between individuals in the composition of the plasma membrane in the cell membrane complex. Genetics appear to be the most important cistron that determines membrane composition, as no or little differences were observed in genetically related pilus samples, rather than external factors such as nutrition or hair care products.

Backdrop of human being hair

The cuticle is the outermost layer formed by flat overlapping cells in a scale-like formation (Robbins, 2012). These cells are approximately 0.5 µm thick, 45–60 µm long and establish at 6–seven µm intervals (Robbins, 2012). The outermost layer of the cuticle, the epicuticle, is a lipo-protein membrane that is estimated to be ten–fourteen nm thick (Swift & Smith, 2001). Beneath that is the A layer with a high cysteine content and a thickness of 50–100 nm, the exocuticle with over again a high cysteine content and a highly variable thickness ranging from 50 to 300 nm, and the endocuticle with a depression cysteine content and a thickness also ranging from 50 to 300 nm.

The bulk of hair fibre is the cortex which contains spindle shaped cells that lie parallel along the fibre axis. These cortical cells were establish to be approximately 1–6 µm in bore and fifty–100 µm in length (Randebrook, 1964). In wool fibres also as human hair, the cortical cells were observed to be divided into different regions termed orthocortex, paracortex and mesocortex (Mercer, 1953). The departure in distribution of these cell types is an important cistron for determining the curvature of the hair fibre (Kajiura et al., 2006). In particular, straight hair tends to take symmetrical distribution of the ortho- and paracortices whereas curly hair tends to accept a non-symmetrical distribution of these cortical cells (Kajiura et al., 2006). Most of the cortical cells are composed of a protein known as keratin (Robbins, 2012).

At the molecular level, keratin is a helical protein (Pauling & Corey, 1950). There are two types of keratin fibres that exist in pilus: blazon I with acidic amino acrid residues and blazon II with basic amino residues. One strand of blazon I fibre and one strand of type Ii fibre screw together to form coiled-coil dimers. In turn, these dimers ringlet together in an antiparallel manner to form tetramers (Crewther et al., 1983; Fraser et al., 1988).

When tetramers are connected from caput to tail, they are known as protofilaments (Robbins, 2012). These tetramers or protofilaments are believed to collaborate together to form a single intermediate filament which is approximately 75–90 Å in diameter. The electric current model of an intermediate filament was proposed in the 1980'south and it involves seven protofilaments surrounding a unmarried cadre protofilament (Robbins, 2012; Fraser et al., 1988). The intermediate filaments then aggregate together to form macro-filaments with a bore of yard to 4000 Å (Robbins, 2012; Randebrook, 1964). Between the intermediate filaments is a matrix consisting of keratin associated proteins, which are irregular in construction. The macro-fibrils consisting of intermediate filaments and the surrounding matrix are the basic units of the cortical jail cell.

The jail cell membrane complex is the material that glues hair cells together. At that place be diverse types of cell membrane complexes: cuticle–cuticle, cuticle–cortex and cortex–cotex depending on the location (Robbins, 2012). The general membrane structure is one 15 nm proteinous delta layer sandwiched by two v nm lipid beta layers (Rogers, 1959). Much speculation still exist regarding the precise structure of the beta and delta layers. However, it has been determined that 18-methyl eicosanoic acid, a covalently bound fatty acid, exists in the upper beta layer in the cuticle–cuticle but not in cortex–cortex membranes (Ward & Lundgren, 1954). In fact, most of the fatty acids in beta layers of membranes in the cuticle–cuticle are covalently jump and nearly of the fatty acids in the beta layers of cortex–cortex are non-covalently jump (Robbins, 2012). Further evidence suggests that the fatty acids in cuticle–cuticle membranes are organized in a monolayer whereas the fatty acids in cortex–cortex prison cell membranes are bilayers (Robbins, 2012). The cuticle–cortex jail cell membrane complex is and then a mixture of the two, with the side facing the cuticle like to cuticle–cuticle membranes and the side facing the cortex similar to cortex–cortex membranes (Robbins, 2012).

Materials and Methods

Training of hair samples

This research was approved by the Hamilton Integrated Enquiry Ethics Board (HIREB) under approval number 14-474-T. Written consent was obtained from all participating individuals. Scalp hair samples were gathered from 12 adults of various historic period, gender, ethnicities, hair colour and pilus curvature. It is of interest to note that there are 3 pairs of study participants with genetic relations including a father and girl, fraternal twins and identical twins. Characteristics of the samples are listed in Table 1.

Tabular array 1

List of all hair samples in this study.

The individuals include men and women and hair of different appearance, such as thickness, color and waviness, and also genetically related hair samples from a male parent and daughter, a pair of identical and a pair of fraternal twins. Labeling agrees with the data shown in Fig. 1.

Subject	Gender	Bore(µm) ± SD	Colour	Appearance	Special comment
i	F	thirty ± 3	light blonde	directly	daughter
ii	M	49 ± 5	brown/grey	curly	male parent
3	F	74 ± 7	black	wavy	–
4	M	50 ± 5	light dark-brown	curly	–
5	F	49 ± 5	blonde	curly	–
half dozen	F	43 ± iv	calorie-free brown	directly	–
seven	F	61 ± 6	lite brown	wavy	–
8	F	49 ± 5	black	wavy	–
9	F	31 ± 3	blonde	wavy	identical twin
x	F	66 ± 7	blackness	straight	fraternal twin
11	F	69 ± 7	black	straight	fraternal twin
12	F	48 ± 5	blonde	curled	identical twin

The pilus samples gathered were cut into strands around three cm long. Care was taken to non stretch or deform the hair strands during this process. For each subject, around 10 strands were taped onto a flexible paper-thin appliance as shown in Fig. 2. The cut-out at the middle of the apparatus is where scattering occurs on the hair sample. The cardboard apparatus is then mounted vertically onto the loading plate of the Biological Big Bending Diffraction Experiment (BLADE) using sticky putty as shown in Fig. 2. All hair samples were measured at room temperature and humidity of 22 °C and 50% RH.

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The apparatus used to mount the hair strands in the experiment.

The paper-thin apparatus is mounted vertically onto the loading plate of the Biological Large Bending Diffraction Experiment (Blade) using sticky putty.

X-ray diffraction experiment

X-ray diffraction data was obtained using the Biological Large Bending Diffraction Experiment (BLADE) in the Laboratory for Membrane and Poly peptide Dynamics at McMaster University. BLADE uses a 9 kW (45 kV, 200 mA) CuKα Rigaku Smartlab rotating anode at a wavelength of 1.5418 Å. Focusing multi-layer eyes provided a loftier intensity parallel axle with monochromatic 10-ray intensities upwardly to 10¹⁰ counts/(southward × mm^two) at the sample position. In order to maximize the scattered intensity, the pilus strands were aligned parallel to the parallel axle for maximum illumination. The slits were set such that nearly 15 mm of the hair strands were illuminated with a width of about 100 µm. The event of this particular beam geometry is seen in the two-dimensional data in Fig. 1: while information technology produces a high resolution along the equator, the master axle is significantly smeared out in the q_z -management up to q_z -values of nigh 0.5 Å^-ane, limiting the maximum appreciable length scale to almost 13 Å.

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2-dimensional X-ray information of all 12 subjects.

The pilus strands were oriented with the long centrality of the hair parallel to the vertical z-axis. The (q _∥, q_z )-range shown was determined in preliminary experiments to embrace the features observable by X-ray diffraction. The measurements cover length scales from about three–ninety Å to study features from the coiled-coil α-keratin phase, keratin intermediate filaments in the cortex, and the membrane layer in the membrane complex. While common features can hands be identified in the 2nd plots, subtle differences are visible, which are discussed in detail in the text.

The diffracted intensity was collected using a point detector. Slits and collimators were installed between X-ray optics and sample, and between sample and detector, respectively. Past aligning the pilus strands in the X-ray diffractometer, the molecular structure along the fibre direction and perpendicular to the fibres could be determined. We refer to these components of the full scattering vector, $\vec{Q}$ , as q_z and q _‖, respectively, in the post-obit. An illustration of q_z and q _‖ orientations is shown in Fig. 3. The result of an 10-ray experiment is a ii-dimensional intensity map of a big area of the reciprocal space of −two.v Å⁻¹ < q_z < ii.v Å^−one and −ii.five Å⁻¹ < q _‖ < 2.five Å⁻¹. The respective real-space length scales are determined by d = 2π/|Q| and encompass length scales from about 3 to xc Å, incorporating typical molecular dimensions and distances for secondary protein and lipid structures.

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Schematics of the X-ray setup and example X-ray data.

The hair strands were oriented in the X-ray diffractometer with their long axis along q_z . Ii-dimensional X-ray data were measured for each specimen covering distances from most 3–ninety Å including signals from the coiled-coil α-keratin stage, the intermediate fibrils in the cortex and from the prison cell membrane circuitous. The 2-dimensional data were integrated and converted into line scans and fit for a quantitative assay.

Integration of the two-dimensional data was performed using Matlab, MathWorks. By adding up the tiptop intensities along the q_z and the q _‖ directions, one-dimensional data along each of the two directions were produced. The q_z intensity was integrated azimuthally for an angle of 25 degrees over the acme. The q _‖ intensity was integrated azimuthally for an bending of 25 degrees over the equator, as depicted in Fig. 3.

The plumbing fixtures process is performed on both the 1-dimensional q_z and the q _‖ information produced from integration. Distinguishable peaks were observed and fitted with the least numbers of Lorentzian superlative functions with an exponential disuse background of the course (a⋅q^b + c) in the first run. Initial Parameters were called based on the observed positions, widths and heights of the peaks and gratuitous to move through the entire q-range. The criterion for the terminal parameters was to minimize the mean square of the difference between data intensity and the fitted intensity. If the fitted intensity cannot conform to the shape of the data intensity, more peaks will be added in the following runs until a skillful fit is acquired. This procedure was repeated for all 12 subjects and performed with trivial or no consultation of previous fittings to minimize bias.

Every bit for the SAXS data, Gaussian functions are used instead. We note that the utilize of optical components in the axle path has an affect on the shape of the observed Bragg peaks: instead of Lorentzian or Bessel peak functions, Gaussian tiptop profiles were establish to best describe the SAXS peaks. The fitting procedure was the same as mentioned before: three Gaussians were fitted to the SAXS data using free-to-motility parameters and an exponential disuse background. However, for some subjects, the 3rd peak was noisy and the least mean square logarithm could not reach a good fit and hence the data was fitted with two Gaussians, only.

Results

A total of 12 adult subjects participated in this study. Details of gender and advent of the hair strands are listed in Table 1. Most ten strands were cut from the scalp, glued onto a sample holder and aligned in the Ten-ray diffractometer. The resulting 2-dimensional Ten-ray intensity maps of the reciprocal space reveal exquisite details of the molecular structure of human scalp hair, as presented in Fig. one. The hair strands were oriented with the long axis of the hair parallel to the vertical z-axis. The displayed (q_z , q _‖)-range was determined to embrace the length scales of the features of interest in preliminary experiments.

The data in Fig. one prove a singled-out not-isotropic distribution of the diffracted intensity with pronounced and well defined intensities along the long axis of the hair and in the equatorial plane (the q_z and q _‖-axes, respectively), indicative of a high degree of molecular order in the hair strands. Some features were common in all specimens and assigned to sure molecular components, equally explained in the side by side department.

Consignment of common handful signals

Coiled-coil protein phase in the cortex

The keratin proteins in the cortex are known to organize in bundles whose structures are dominated by α-helical coiled-coils (Pauling & Corey, 1950; Pinto et al., 2014; Yang et al., 2014). The primary features of this pattern are a ∼9.5 Å (corresponding to q _‖ ∼ 0.6 Å^−ane) equatorial reflection corresponding to the spacing between adjacent coiled-coils and a ∼v.0 Å meridional reflection (corresponding to q_z ∼ 1.25 Å⁻¹) corresponding to the superhelical construction of α-helices twisting around each other within coiled-coils (Crick, 1952; Cohen & Parry, 1994; Lupas & Gruber, 2005). Equally displayed in Fig. four, these signals were observed in the X-ray data in all specimen and assigned to the coiled-ringlet protein phase. Nosotros note that these peaks are related to generic α-helical coil structures of monomeric proteins, and not specific to a certain type of protein.

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The hierarchical construction of hair in the cortex and cuticle.

The main component of the cortex is a keratin coiled-scroll poly peptide phase. The proteins grade intermediate filaments, which then organize into larger and larger fibres. The hair is surrounded by the cuticle, a dead jail cell layer. The common features observed in the X-ray data of all specimens are signals related to the coiled-coil keratin stage and the formation of intermediate filaments in the cortex, and the jail cell membrane complex. Bespeak assignment and corresponding length scales are shown in the figure.

Lipids in the prison cell membrane complex

The prison cell membrane complex mainly consists of lipid mono- and bilayers. The corresponding scattering features correspond to a lamellar periodicity of about 45 Å, and rings at spacings of about four.3 Å, characteristic of the lodge within the layers (Busson, Engstrom & Doucet, 1999). Both these features are observed in the 2-dimensional X-ray data of all individuals in Fig. one, as a ring-like scattering intensity at q-values of ∼0.1 Å^-1 and a wide, ring-similar scattering at ∼i.five Å^-1 every bit a result of the lipid social club inside the membrane layers. The corresponding diffraction point has a maximum on the q_z -centrality, indicating a preferential orientation of the membrane aeroplane parallel to the surface of the hair.

Intermediate filaments in the cortex

The keratin coils organize into intermediate filaments whose structure and packing in the plane of the hair result in additional scattering signals. The packing of these fibrils by bundling into macro-fibrils is characterized past X-ray diffraction pattern by three equatorial spots located at about ninety, 45 and 27 Å (Busson, Engstrom & Doucet, 1999). The respective signals are observed in the 2-dimensional information in Fig. i. The exact position of the features is, however, best determined in small angle diffraction experiments (SAXS), which offer a drastically improved resolution, and will be shown below. We note that the axial packing of coiled-coils within keratin filaments in hair gives rise to a number of fine arcs along the meridian (z). The typically observed signal on the tiptop at 67 Å, which arises from the axial stagger between molecules along the microfibril (Briki et al., 2000; Rafik, Doucet & Briki, 2004), could not exist observed in our experiments due to the relaxed resolution of the parallel axle in this management. While the features observed in scattering experiments are well known, the molecular compages of the intermediate filaments is still nether discussion (Rafik, Doucet & Briki, 2004). Supercoiled coiled-coils or models that involve straight dimers with different numbers of coils are being discussed.

The three features in a higher place were observed in all individuals in Fig. 1. The underlying molecular structures will be quantitatively analyzed in the side by side section (Quantitative analysis of handful results). Nosotros note that additional features are seen in some of the measurements in Fig. 1, mainly in the broad membrane band at effectually i.5 Å^-1 which indicates a difference in molecular composition of the jail cell membrane complex betwixt individuals. We will come dorsum to these differences in the Give-and-take.

Quantitative analysis of scattering results

In order to quantitatively determine the position of the corresponding handful features, the 2-dimensional data for all 12 individuals were integrated in the equatorial plane (q _‖-axis) of the hair fibres, and along the hair fibres (q_z -axis). The resulting plots are shown in Fig. 5. In the direction along the hair fibre axis (q_z ), at that place are two major peaks that were consistent amid all subjects, one narrow tiptop effectually five.0 Å and ane broader top around 4.3 Å.

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Integration of the ii-dimensional scattering data in Fig. 1 in the equatorial plane (q _‖) (A), and along the axis of the hairs (q_z ) (C), respectively, for all subjects. The 2 signals present in all individuals in the equatorial airplane (q _‖) correspond to the distance between two coiled coils of 9.5 Å and between ii lipid tails in the cell membrane cortex of 4.3 Å. The common meridional signal forth the long axis of the hair (q_z ) at 5 Å corresponds corresponds to the α-helices twisting around each other within coiled-coils. Average values and standard deviations are in (B).

In the management perpendicular to the hair fibre centrality (q _‖), there are likewise two major peaks consistent amid all subjects, one narrow peak around 9.five Å and i wide summit around four.3 Å. The total handful contour was well fit by two Lorentzian top profiles (and a background), whose positions is plotted in Fig. 5. The signals at v.0 Å and 9.5 Å are in excellent agreement with signals reported from coiled-coil keratin proteins (Pauling & Corey, 1950), as depicted in the Figure. The wide signal at virtually four.3 Å present in both directions is due to the band-like scattering from the lipids in the membrane component. As plotted in Fig. v, there is a narrow distribution of the respective length scales with standard deviations of ix.51 ± 0.07 Å and 5.00 ± 0.02 Å for the keratin coiled-coils and 4.28 ± 0.08 Å for the membrane signal, indicating that the common features observed in all individuals are well defined with picayune spread in the corresponding molecular dimensions.

Due to the big length scales involved, the signals from intermediate filaments occur at pocket-sized handful vectors, shown in Fig. 6. The Small Bending 10-ray Handful (SAXS) profile was well fit with 3 Gaussian peaks at xc Å, 45 Å, and 27 Å. We note that the third summit was not observed in all pilus samples. The corresponding top positions and distributions are shown in the figure. The 90 Å peak has been reported early in the literature every bit the distance between intermediate filaments in human hair. As further elaborated by Rafik, Doucet & Briki (2004), these peaks correspond to the radial structures of the intermediate filaments and can exist well-simulated by assuming parallel tetramers formed by 2 coiled-coils with a slight disorder in positions and orientations, as depicted in the figure. Also here, the standard deviations of 90 ± 2 Å, 47 ± 2 Å, 27 ± 1 Å, equally shown in the figure, are pocket-size, indicating that the organization of the intermediate filaments on the nanoscale varies very little between different individuals.

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Diffraction features at small scattering angles.

The small-scale q _‖-range is shown in magnification in (A). The specimen of most individuals showed 3 distinct reflections at ∼90 Å, 46.5 Å and 27 Å, related to the properties of intermediate keratin filaments (B).

Word

All hair used in this study was in its native country, collected from salubrious individuals and not chemically treated prior to the experiments. However, all individuals regularly used shampoos for cleaning and boosted products such as conditioners, wax and gel. These products function primarily at or near the cobweb surface to remove dirt from the hair surface, for case, and do non seem to have an impact on the internal keratin structure, as will be discussed below.

An aberrant signal was previously reported by James et al. (1999) in pilus samples of patients with chest cancer. Such an approach is quite intriguing, as scanning of hair samples could be used as easy, inexpensive and non-invasive screening techniques in the diagnosis of cancer. James et al. (1999) observed a ring-similar signal at 44.4 Å, at the position of the lamellar plasma membrane signal, and assigned this point to the presence of breast cancer. The assay and assignment was questioned later on by Briki et al. (1999) and Howell et al. (2000), who observed this feature in salubrious and cancer patients in equal measure. The ring-like 45 Å signal is also present in the information for all individuals included in our study, such that a relation to breast cancer can near likely be excluded.

General structural features from the X-ray experiments

From the 2-dimensional X-ray information in Figs. 1 and 4, and the analysis in Figs. five and half-dozen, we identify three features nowadays in all individuals. These signals are related to the coiled-coils arrangement of the keratin proteins in the cortex, the germination of intermediate filaments in the cortex, and lipids in the prison cell membrane complex of the hair. Statistical assay of the corresponding molecular dimensions revealed a rather small distribution between different individuals. These general properties of human pilus are observed in all pilus independent of gender, colour or optical advent of the hair (as listed in Table one) within the number of individuals included in this study.

Differences in the X-ray data between individuals were observed in the wide angle region (WAXS) of the ii-dimensional data in Fig. 1, related to backdrop of the membrane component. Figure 7A shows a comparing between individual 3 and 4 to illustrate the effect. For an easy comparison, the original data were cut in half and recombined, such that the left half depicts private 3, and the right half private 4. While signals from the coiled-coil protein phase, the diffuse, ring-like intensity from lipids in the jail cell membrane circuitous and the modest bending signals due to the formation of intermediate filaments are observed in both individuals, boosted signals occur in Discipline 3 around the position of the membrane-ring. Almost identical patterns are observed in Figs. 7B and 7C, while differences are seen in Fig. 7D; this volition be discussed in detail beneath.

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Comparing betwixt hair samples.

(A) shows a comparison betwixt individuals 3 and 4. While the two specimens both show the general features, differences are observed in the region of signal from the cell membrane complex. (B) Comparison between individuals 1 and ii, father and daughter. The data in (C) (individuals ix and 12) are from identical twins. Information in (D) was taken from fraternal twins (individuals 10 and 11). While different individuals in full general show different membrane patterns (A), features in (B) and (C) perfectly concur. Fraternal twins show slight differences in their blueprint in (D).

The boosted signals observed between nearly ane.34 Å^-1 and 1.63 Å^-i can be assigned to fatty acids located within the plasma membrane of the jail cell membrane circuitous. The position of these lipids inside the hair was determined by synchrotron infrared microspectroscopy (Kreplak et al., 2001a) detecting the corresponding CH₂ and CH_iii bands. The lipid component of the cell membrane complex consists of three major classes of lipids: glycerolipids (mainly phospholipids), sterols and sphingolipids (Furt, Simon-Plas & Mongrand, 2011). The nearly arable lipid species are referred to equally structural lipids up to 80% of which are phosphocholine (PC) and phosphoethanolamine (PE) phospholipids.

The position and width of the broad, ring-like intensity observed in all specimens in Fig. ane hold well with lipid correlation peaks reported from unmarried and multi-component phospholipid fluid lipid membranes (Kučerka et al., 2005; Petrache et al., 1998; Kuč, Tristram-Nagle & Nagle, 2006; Rheinstädter et al., 2004; Rheinstädter, Seydel & Salditt, 2007; Rheinstädter et al., 2008; Pan et al., 2008; Schneggenburger et al., 2011; Harroun et al., 1999) and diffraction observed in plasma membranes (Welti et al., 1981; Poinapen et al., 2013). The broad correlation peak is the tell-tale sign of a fluid-like, disordered membrane structure. It is related to the packing of the lipid tails in the hydrophobic membrane core, where the lipid acyl chains form a densely packed construction with hexagonal symmetry (planar grouping p6) (Armstrong et al., 2013). The distance between two acyl tails is determined to be $a_{T} = 4 π / (\sqrt{3} q_{T})$ (Mills et al., 2008; Barrett et al., 2012; Barrett et al., 2013), where q_T is the position of the membrane correlation peak. The average nearest-neighbour altitude betwixt ii lipid tails is calculated from the peak position to 4.97 Å. We notation that the intensity of the disordered membrane component is not distributed isotropically on a circumvolve, which would exist indicative of a non-oriented, isotropic membrane phase. The corresponding scattering signal has a maximum along the q_z -axis, indicative that most of the membranes are aligned parallel to the hair surface.

The additional narrow components in Fig. 1 between virtually 1.34 Å^-1 and 1.63 Å^-1, which are observed in some pilus samples, agree with structural features reported in lipid membranes of different limerick. A correlation pinnacle at ∼i.5 Å^-ane was plant in the gel phase of saturated phospholipid membranes, such as DMPC (Dimyristoyl-sn-glycero-iii-phosphocholine) and DPPC (Dipalmitoyl-sn-glycero-3-phosphocholine) (Tristram-Nagle et al., 2002; Katsaras et al., 1995; Rheinstädter et al., 2004). Unsaturated lipids were reported to order in a structure with slightly larger nearest neighbour tail distances, leading to an acyl-chain correlation meridian at ∼1.3 Å^-1, every bit reported for DOPC and POPC (Mills et al., 2009), for instance. Lipids, such every bit Dimyristoylphosphatidylethanolamine (DMPE) and the charged DMPS (Dimyristoyl-sn-glycero-3-phosphoserine) with smaller caput groups were reported to order in more densely packed structures (Rappolt & Rapp, 1996). The corresponding acyl concatenation correlation peaks were observed at Q values of ∼ i.65 Å⁻¹. The observed differences in the X-ray diffraction patterns between dissimilar individuals tin, therefore, virtually likely be assigned to differences in the molecular composition of the plasma membrane in the cell membrane circuitous. Genetics plays an important function in this composition.

Genetic similarity

Some subjects have genetic relations inside the subject puddle. In particular, Subject one and 2 are daughter and father, Subjects ten and 11 are fraternal twins, and Subjects 9 and 12 are identical twins. The corresponding diffraction data are shown in Figs. 7B, 7C and 7D. While in general, the diffraction patterns in the membrane region were found to be different (as demonstrated in Fig. 7A), the genetically similar hair of father and girl and identical twins bear witness identical patterns within the resolution of our experiment.

It is interesting to note that differences are observed for the fraternal twins in Fig. 7D. This finding is in agreement with the expectation that individuals with similar genetics would share similar physical traits such every bit hair construction. Identical or monozygotic twins originate from one zygote during embryonic development, and they share 100% of their genetic material. Congenial or dizygotic twins develop from the fertilization of 2 different eggs and they only share 50% of their Dna on average (Nussbaum et al., 2007).

As expected, the identical twin pair shows almost identical hair structures whereas the fraternal pair exhibits distinct differences. Offspring receive one-half of their chromosomes from each parent, thus the genetic similarity between the parent and child pair is roughly the same as fraternal twins (Creasy et al., 2013). It is, therefore, surprising that the male parent and daughter pair share significantly more similarities than the pair of congenial twins. This tin can be attributed to the fact that the expression of a complex trait such as hair construction would depend on the inheritance pattern of many phenotype-determining genes, such as whether they are dominant or recessive traits. Genetic similarity does not guarantee identical hair structure and similarly, genetic variability does non guarantee differences. While we tin can report this finding, the minor number of related samples excludes a more detailed and quantitative analysis of this outcome at this time.

The comparison in Fig. 7B between father and girl as well enables the written report of the effect of hair care products, such every bit shampoo and conditioner on the molecular structure of hair. While Discipline 2 (father) uses soap and shower gel to clean scalp and hair, Subject 1 (daughter) regularly uses shampoo and conditioner. The identical Ten-ray signals signal that these products exercise not have an effect on the molecular construction of keratin and membranes deep inside the pilus (within the resolution of our experiment).

Nosotros note that in order to maximize the scattered signals, the entire hair strand was illuminated in our experiments using a relatively large X-ray beam. Microbeam X-ray diffraction on synchrotron sources, which uses small, micrometre sized beams (Iida & Noma, 1993; Busson, Engstrom & Doucet, 1999; Kreplak et al., 2001b; Ohta et al., 2005; Kajiura et al., 2006), gives a high spatial resolution. By illuminating selective parts of the hair, the occurrence of the signals that we observed can be determined as a function of their location within the pilus in future experiments.

Conclusions

We studied the molecular pilus structure of several individuals using X-ray diffraction. Hair samples were collected from 12 healthy individuals of various characteristics, such as gender, optical appearance and genetic relation. Signals corresponding to the coiled-roll phase of the keratin molecules, the formation of intermediate filaments in the cortex and from the lipid molecules in the prison cell membrane complex were observed in the experiment. The respective signals were observed in all individuals, independent of gender or appearance of the hair, such as color or waviness, within the resolution of this experiment. Given the minor standard departure of the molecular dimensions of these general features, anomalies possibly related to certain diseases should be easy to notice.

While all hair samples showed these general features, differences between individuals were observed in the composition of the plasma membrane in the prison cell membrane complex. Genetics seem to play an important role in the properties of these membranes, as genetically similar pilus samples from father and girl and identical twins showed identical patterns, though hair from congenial twins did not.

Funding Argument

This research was funded by the Natural Sciences and Applied science Research Council of Canada (NSERC), the National Research Quango Canada (NRC), the Canada Foundation for Innovation (CFI) and the Ontario Ministry of Economical Development and Innovation. MCR is the recipient of an Early Researcher Award of the Province of Ontario. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Additional Information and Declarations

Competing Interests

The authors declare there are no competing interests.

Author Contributions

Fei-Chi Yang, Yuchen Zhang and Maikel C. Rheinstädter conceived and designed the experiments, performed the experiments, analyzed the information, contributed reagents/materials/assay tools, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.

Human Ethics

The following information was supplied relating to ethical approvals (i.e., approving trunk and whatsoever reference numbers):

Hamilton Integrated Enquiry Ideals Board (HIREB) under approval number fourteen-474-T.

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