Keratin associated proteins

Another example of a quantal repeat—but with considerable variation in sequence—is seen in the keratin-associated proteins (KAPs). In sheep, these display pentapeptide and decapeptide consensus repeats of the form G—G—Q—P—S/T and C-C-Q/R—P—S/T—C/S/T—C—Q—P/T—S, respectively (Parry et al., 1979). Some of the positions, as indicated by the presence of a consensus sequence, contain residues that occur much more frequently than others, but the absolute conservation of a residue in any position is not observed. The decapeptide consists of a pair of five-residue repeats closely related, but different to that displayed by the pentapeptide. Although the repeats have an undetermined structure, the similarity of the repeat to a sequence in snake neurotoxin suggests that the pentapeptides will adopt a closed loop conformation stabilized by a disulphide bond between cysteine residues four apart (Fig. 5 Fraser et al., 1988 Parry et al, 1979). Relative freedom of rotation about the single bond connecting disulphide-bonded knots would give rise to the concept of a linear array of knots that can fold up to form a variety of tertiary structures. The KAPS display imperfect disulphide stabilization of knots and have interacting... 

Fig. 5. Predicted conformation of the pentapeptide repeat C-X-Y-Z-C in trichocyte keratin-associated proteins. Glutamine and arginine residues are found commonly in the X position, prolines in the Yposition, and serines and threonines in the Z position. The structure is based on the known conformation of a similar repeat in snake neurotoxin. The model shows a disulphide bond-stabilized /5-bend with a potential hydrogen bond (dotted). A string of these /5-bends, linked by bonds about which there is relatively free rotation, has been proposed as a model for this important family of matrix proteins in trichocyte keratin (Fraser et al, 1988). Figure from Fraser et al (1988) with permission from Elsevier.

A portion of the undermembrane of Figure 1-21 is also epicuticle. The cystine-rich proteins of the cuticle belong to the group of proteins called keratin-associated proteins. Although structurally different, keratin-associated proteins are also found in the matrix of the cortex. See the section that discusses keratin-associated proteins in Chapter 2. For more details of the intercellular structures, see Figure 1-23. Thus, the cuticle of human hair is a laminar structure similar to the cuticle of wool liber, and the different layers of the cuticle have been described for merino wool [64] and for human hair [58, 65, 66, 67], Figures 1-23 and 1-24 illustrate the... 

By analogy with the effects of malnutrition and sulfur enrichment on the high-sulfur proteins of the keratin-associated proteins in wool fiber [44,45], these effects of a lower cystine content in hair are probably a result of a decreased synthesis of the sulfur-rich proteins because of malnutrition. Studies of the effects of diet in persons suffering malnutrition (i.e., protein deficiencies) show that diet supplementation can influence the protein composition of human hair. However, such effects have only been demonstrated among persons suffering from severe malnutrition and never among healthy persons on a normal diet see the section on the keratin-associated proteins of human hair later in this chapter. 

KAP, keratin-associated proteins (formerly IFAP intermediate filament-associated proteins)... 

Morphologically, the fibres are composed of the cortex and the cuticle. Each of the two components is formed of various other morphological components (Table 9.6.3). The cortex contains cortical cells and the cell membrane complex. The cortical cell is further composed of macro-fibrils and intermacro-fibrillar material. The macro-fibrils consist of micro-fibrils and intermicro-fibrillar matrix. In summary, the cortex is formed of micro-fibrils (intermediate filament, IF, or keratin proteins, KP) and keratin associated proteins (IFAP or KAP), which compose the intermicrofibrillar matrix containing cytoplasmatic and nuclear remnants. This ensemble is wrapped up in the cuticle, as an external sheath which also has its own architecture, being formed of four layers the epicuticle, the a-layer, the exocuticle and the endocuticle. 

Wool and hair have the most complex structures of any textile fibres. In the paper by Viney, fig. 1 shows how keratin proteins, of which there are more than one type, all having a complicated sequence of amino acids, assemble into intermediate filaments (IFs or microfibrils). But, as shown in Fig. 5a, this is only one part of the story. The microfibrils are embedded in a matrix, as shown in Fig. 5b. The keratin-associated proteins of the matrix contain substantial amounts of cy.stine, which cross-links molecules by -CH2-S-S-CH2- groups. Furthermore, terminal domains (tails) of the IFs, which also contain cystine, project into the matrix and join the cross-linked network. At a coarser scale, as indicated in Fig. 5c, wool is composed of cells, which are bonded together by the cell membrane complex (CMC), which is rich in lipids. As a whole, wool has a multi-component form, which consists of para-cortex, ortho-cortex, meso-cortex (not shown in Fig. 5a), and a multi-layer cuticle. In the para-and meso-cortex the fibril-matrix is a parallel assembly and the macrofibrils, if they are present, run into one another, but in the ortho-cortex the fibrils are assembled as helically twisted macrofibrils, which are clearly apparent in cross-section.s. 

Parry DAD et al. (2006) Human hair keratin-associated proteins sequence regularities and stractural implications. J Struct Biol 155(2) 361-369... 

Another important natural fibrous material is wool. Wool is mainly made of proteins called keratins. Not a single kind, but several different keratins are involved acidic and basic keratins and keratin-associated proteins. Keratins are related to silk fibroin mentioned earlier. Both a-helix and P-pleated structures of keratin are involved. The keratin-associated proteins contain high level of the sulfur-containing amino acid, cysteine. The sulfhydryl (-SH) group of cysteine can readily be oxidized and combine with another sulfhydryl sulfur atom of another cysteine residue on another polypeptide. The result is the formation of sulfur-sulfur... 

Human hair is essentially the same as wool. It is made of keratins and keratin-associated proteins. When you have your hair set, the chemistry mentioned in the last paragraph is made use of. First your hair will be treated with a smelly jerry kind of... 

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