Structure of Keratins

Figure 7-31 A model for the structure of keratin microfibrils of intermediate filaments. (A) A coiled-coil dimer, 45-nm in length. The helical segments of the rod domains are interrupted by three linker regions. The conformations of the head and tail domains are unknown but are thought to be flexible. (B) Probable organization of a protofilament, involving staggered antiparallel rows of dimers. From Jeffrey A. Cohlberg297...

FIGURE 24.7 Then-helical secondary structure of keratin. The amino acid backbone winds in a spiral, much like that of a telephone cord. 

Steinert, P. M., Marekov, L. N., and Parry, D. A. D. (1993b). Conservation of the structure of keratin intermediate filaments Molecular mechanism by which different keratin molecules integrate into pre-existing keratin intermediate filaments during differentiation. Biochemistry 32, 10046-10056. 

Figure 2.25. Structure of keratin protofibrils. The diagram illustrates the structure of keratin in intermediate filaments containing a helical sequences. Two coils are wound around each other and then packed into protofilaments. Eight protofilaments are packed into a filament.

VI. Relationship between the Physical Properties and Chemical Structure of Keratin... 

This section is concerned primarily with the effects of chemical modifications of keratins on their physical properties—supercontraction, setting, swelling, load-extension characteristics, and other mechanical properties. Much of this work could be described by the term mechanochemical coined by Speakman (1947). The complexity of the cellular and sub-cellular structure of keratins necessitates the use of simplifying assumptions in the interpretation of mechanochemical experiments. 

Hair is composed of a protein called keratin. The secondary structure of keratin is a-helix throughout, meaning that the protein has a wound-up helical structure. As we learned earlier, this structure is maintained by hydrogen bonding. 

After the structure of keratin in the wool is loosened by breaking the disulfide bonds, extracellular proteolytic enzymes hydrolyze the peptide bonds as shown in Fig. 1.4. The hydrolysis releases soluble peptides that are further hydrolyzed to amino acids. 

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... 

Fibrillar proteins have a specific secondary structure. For example, the basic secondary structure of keratin consists of two pairs of closely linked right-handed a-hehces (a superhehx) that are coiled into a left-handed hehx. The basic secondary structure of collagen is a triple hehx in which the left-handed polypeptide helix is coiled into the right-handed superhehx. 

FIGURES. 7. Structure of keratin and example of hair extensions (Wikimedia Commons). 

In the primary structure of keratine, serine is the N-end group, and tyrosine is C-end group. In this connection, reduction of the quantity of these amino acids testifies degradation of the primary stmcture of the protein. 

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