MOLECULAR MODELING OF HUMAN HAIR 471 top surface plane XY of the beta sheet folds). The 18-MEA molecules were then allowed to move and relax using an NVT ensemble MD simulation for a 120-ps time period. The result of this simulation, followed by energy minimization, was the well-relaxed virgin hair sur- face, and is shown in molecular graphics views in Figures 3–5. The snapshot shown in Figure 4 is at the end of 120 ps of MD simulation wherein the 18-MEA chains are quite coiled conformationally and packed nicely into a fi lm or monolayer without any signifi cant van der Waals gaps. The fi nal thickness of the 18-MEA layer came to be 1.08 nm. Figure 4. Energy-minimized structure of 18-MEA attached to a beta sheet of a KAP-5 protein to represent the lipid layer attached to the backbone of the cuticle cell membrane of a keratin fi ber. Figure 3. Schematic representation of the beta sheets setup of the epicuticle molecular model.

JOURNAL OF COSMETIC SCIENCE 472 Various models (up to fi ve) of the protein sequencing in the beta sheet were arrived at by a specifi c choice of particular cysteines that can take part in the linking to 18-MEA at the top folds. Of these representative, and possibly stereochemically different, arrangements of amino acids with respect to the top folds (i.e. with respect to the top plane of the hair sur- face), one model was chosen, which is depicted in Figure 1 for its protein sequence as well as the cysteines that take part in linkage with 18-MEA on the top folds. All studies were performed with this uppermost model of the epicuticle hair surface. RESULTS AND DISCUSSION The exact UHSP that 18-MEA is attached to is not known at this time, but a likely possibility is from the KAP-5 family of cuticle proteins (10,11). Human KAP-5 se- quences that we considered for modeling are the one from Yahagi et al. (9) and the one by McKinnon et al. (13). The Yahagi et al. UHSP provided the composition as cystine (35%), Figure 5. Views of the virgin hair surface from molecular modeling: (A) Diagonal view of 18-MEA on the UHSP surface (spacing is 1 nm × 0.7 nm (lattice)). (B) Schematic: Initial atomic structure. 18-MEA not re- laxed to equilibrium. (C) Close-up view of top fold and MEA. (D) Close-up of top fold and 18-MEA. Side view looking between the beta sheets.