A detailed mapping of the readily accessible disulfide bonds in the
cortex of wool fibers
Abstract
One way in which trichocyte keratin intermediate filament proteins
(keratins) and keratin associated proteins (KAPs) differ from their
epithelial equivalents is in their higher levels of cysteine residues.
Interactions between these cysteine residues within a mammalian fiber,
and the putative regular organization of interactions (i.e., types of
disulfide bond) 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 explore a finer set of levels
associated with interactions between keratins and KAPs. We found that
most of the cysteines in the KAPs were close to either the N- or C-
terminal domains of these proteins. The most accessible cysteines in
keratins were present in the head or tail domains indicating their
function in readily forming intermolecular bonds with KAPs. Some of the
more buried cysteines in keratins were discovered either close to or
within the rod region in positions previously identified in human
epithelial keratins as being involved in crosslinking between the
heterodimers of the tetramer. Our present study therefore provides a
deeper understanding of the accessibility of disulfides especially in
keratins and thus proves that there is some specificity to the disulfide
bond interactions leading to these intermolecular bonds stabilizing the
fiber structure.