Photon Factory Activity Report 2004 #22 Part B (2005)
Biological Science

4A, 15A/2002G343

Structural Analysis of a Single Keratin Fiber by Scanning Microbeam SAXS
Yoshio KAJIURA1, Shunichi WATANABE1, Takashi ITOU1,Yuya SHINOHARA2, Yoshiyuki AMEMIYA*2
1
Kao Corporation, 2-1-3 Bunka, Sumida-ku, Tokyo 131-8501, Japan2
Department of Frontier Sciences, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba, Japan
Introduction
The nano structure of a single wool fiber has beenstudied by scanning microbeam SAXS to reveal therelationship between the lateral inhomogeneity of keratin
structure and the curl shape of a fiber. A wool fiber has astrong curl shape and is mainly composed of cuticle andcortex. The cortex consists mainly of the crystalline αkeratin filaments (Intermediate Filaments:IFs) embeddedin the amorphous matrix protein (Keratin AssociatedProtein:KAP). Most wool fibers contain two (sometimesthree) types of cortical cells, so called orthocortex andparacortex (and mesocortex), and the bilateralarrangement of them (usually orthocortex and paracortex)
is associated with the crimped structure of wool fibers [1].
It has been found that there are obvious differences in thegeometrical arrangement of the IFs among these corticalcells. The purpose of our study is to analyze theinhomogeneity in the IF distribution of a single bilateralwool fiber in intact condition by measuring SAXS
patterns with an X-ray microbeam scanning from theinner to the outer sides of the curved fiber. In the firstyear, we optimized experimental conditions to improve
Signal / Noise (S/N) ratio of measured SAXS patterns,and succeeded in detecting the difference of the intensity
profile between orthocortex and paracortex. We havemade further optimization of experimental conditions inorder to evaluate quantitatively the IF distribution in thecortex by the calculation of the equatorial intensity
profiles based on the IF distribution model
Experimental
SAXS patterns from a Merino wool were measured at
BL-4A. They were measured with a X-ray microbeam(size : 5µm) scanning with a 5µm step from outer to innersides of a curved fiber (A single Merino wool fiber hasaround 30µm diameter).
Results and DiscussionWe extracted the equatorial intensity profiles of thecortex from the 2-dimensional SAXS patterns after
subtraction of the parasitic scattering and compared thesewith those calculated based on the IF distribution model
proposed by Briki et al.[2]. Then the IF diameter and themean IF-IF distance, which are included in the model asparameters, are determined by the least square method.
Figure 1 shows one example of the results. The
experimental data were obtained from the SAXS patternmeasured at the inner side of the cortex (the black
coloured points were used for fitting). The simulated
curve (red line) is found to be in good agreement with theexperimental data. Figure 2 shows the results of IF
diameters and IF-IF distances calculated from three fibers.

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It is found that the IF-IF distance increases from c.a. 80Å
at the outermost to c.a. 95Å at the innermost of the curved
fiber while the IF diameter has an almost constant value(c.a. 75Å). These tendencies are in good accordance withthe results of previous work that the ratio of KAP/IFs ishigher in the paracortical cells than that in theorthocortical cells [3]. From this study, we could not only
evaluate the IF diameter and the IF-IF distance of a wool
fiber in intact condition but also show quantatively thedifferences of them between orthocortex and paracortex
at the first time.

Fig.1 Experimental data and the result of calculationof an equatorial intensity profile of the cortex

Fig.2 IF diameter and IF-IF distance along a lateral
direction of a wool fiber
References[1] J. H. Bradbury, Advances in Protein Chemistry.
Academic Press, 27, 111, (1973).
[2] Fatma Briki et al., Biochimica et Biophysica Acta,1492 (1998).
[3] H.Sakabe et al., SEN-I GAKKAISHI 45, 388 (1989).
amemiya@k.u-tokyo.ac.jp