Identification of the intermediate filament proteins (IFPs) in the wool proteome has formerly been hampered by limited sequence information, the high degree of IFP homology and their close proximity on 2-DE maps. This has been partially rectified by the recent acquisition of four new Type I and two Type II wool IFP sequences. Among closely migrating proteins, such as IFP clusters in a 2-DE map, proteins with higher sequence coverage will be assigned higher scores, but the identification of unique peptides in such tight clusters may distinguish these closely migrating proteins. Two approaches were adopted for the study of wool IFPs. In the first, searches were conducted for peptides known to be unique to each member of the family in each spot. In the second, MALDI imaging was employed to examine peptides bound to a PVDF membrane from a poorly resolved part of the Type I IFP region of the 2-DE map. As a result, a distinct picture has emerged of the distribution of the six Type I and four Type II IFPs across the 2-DE wool protein map.
Sheep wool has traditionally been viewed as the representative mammalian keratin fiber for the purposes of describing morphology and protein composition. We have investigated narrow fibers from the under-hairs of a range of species both closely and distantly related to sheep, comparing structure and protein composition. Within this group, curvature was negatively correlated with diameter for all but mohair. The cortical cell types present in alpaca, rabbit, and mohair fibers differed structurally from wool, primarily in terms of their macrofibril architecture. Except for rabbit, each species' fibers contained three cell types, and except for mohair, cell types were distributed asymmetrically across the cortex. In mohair, the cell types were distributed annularly, and each cell type had regions in which intermediate filaments were packed into highly aligned hexagonal mosaics, much like the mesocortex in wool. Coupled with this, were differences in the protein profiles; the rabbit fiber contained extra keratins and keratin associated proteins, while only subtle differences were noted between mohair and Merino fibers. In both rabbit and mohair fibers, the relative abundance of keratin K85 was lower than that of Merino. These results suggest that there may be links between relative protein composition and fiber morphology, albeit complex ones.
We provide a detailed description of the ultrastructure of deer hair fibers. Guard hairs and underhairs from the winter coat of red deer (Cervus elaphus), and antler velvet hairs from the same species were examined. All fibers displayed the typical keratin fiber morphology of overlapping cuticle cells surrounding a core of cortex cells, and often a centrally-located medulla, but there were considerable differences in the diameter, cuticle thickness, and scale pattern, and in the relative amounts of cortex and medulla along individual fibers, and between the different types of fiber. In addition, closer examination of cortex cells using transmission electron microscopy revealed considerable differences in the arrangement of intermediate filaments in the different fiber types. Fine underhairs appeared similar to fine wool fibers from sheep because intermediate filament arrangements were very similar to those found in wool orthocortex cells and paracortex cells. In addition, a similar bilateral distribution of these cell types was evident. However, in the antler velvet hairs and the guard hairs, intermediate filament arrangements were more variable and complex, and showed similarities to those in heterotype cortex cells described for human hair.
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