Trichocyte keratin intermediate filament proteins (keratins) and keratin associated proteins (KAPs) differ from their epithelial equivalents by having significantly more cysteine residues. Interactions between these cysteine residues within a mammalian fiber, and the putative regular organization of interactions are likely important for defining fiber mechanical properties, and thus biological functionality of hairs. Here we extend a previous study of cysteine accessibility under different levels of exposure to reducing compounds to detect a greater resolution of statistically non‐random interactions between individual residues from keratins and KAPs. We found that most of the cysteines with this non‐random accessibility in the KAPs were close to either the N‐ or C‐ terminal domains of these proteins. The most accessible non‐random cysteines in keratins were present in the head or tail domains, indicating the likely function of cysteine residues in these regions is in readily forming intermolecular bonds with KAPs. Some of the less accessible non‐random cysteines in keratins were discovered either close to or within the rod region in positions previously identified in human epithelial keratins as involved in crosslinking between the heterodimers of the tetramer. Our present study therefore provides a deeper understanding of the accessibility of disulfides in both keratins and KAPs and thus proves that there is some specificity to the disulfide bond interactions leading to these inter‐ and intra‐molecular bonds stabilizing the fiber structure. Furthermore, these suggest potential sites of interaction between keratins and KAPs as well as keratin‐keratin interactions in the trichocyte intermediate filament.

中文翻译：

---

羊毛纤维皮层中易于接近的二硫键的详细映射

毛细胞角蛋白中间丝蛋白（角蛋白）和角蛋白相关蛋白 (KAP) 与它们的上皮等效物不同，因为它们具有明显更多的半胱氨酸残基。哺乳动物纤维中这些半胱氨酸残基之间的相互作用，以及假定的相互作用的规律组织，对于定义纤维机械特性以及毛发的生物学功能可能很重要。在这里，我们扩展了先前对不同水平的还原性化合物暴露下半胱氨酸可及性的研究，以检测角蛋白和 KAP 的各个残基之间的统计非随机相互作用的更大分辨率。我们发现 KAP 中大多数具有这种非随机可及性的半胱氨酸靠近这些蛋白质的 N 端或 C 端结构域。角蛋白中最容易接近的非随机半胱氨酸存在于头部或尾部结构域，表明这些区域中半胱氨酸残基的可能功能是很容易与 KAP 形成分子间键。角蛋白中一些不易接近的非随机半胱氨酸被发现靠近或位于杆状区域内，这些位置先前在人类上皮角蛋白中被确定为参与四聚体异二聚体之间的交联。因此，我们目前的研究提供了对角蛋白和 KAP 中二硫键的可及性的更深入理解，从而证明二硫键相互作用存在一些特异性，导致这些分子间和分子内键稳定纤维结构。此外，