Keratin

From Encyclopedia Jr, free information reference for Kids

Distinguish from kerogen.

Microscopy of keratin filaments inside cells.

Keratins are a family of fibrous structural proteins; tough and insoluble, they form peptide bonds to adjacent protein chains, facilitating their close alignment of the sulfur-containing amino acid cysteine, required for the disulfide bridges that confer additional strength and rigidity by permanent, thermally-stable crosslinking — a role sulfur bridges also play in vulcanized rubber. Human hair is approximately 14% cysteine. The pungent smells of burning hair is due to the sulfur compounds formed. Extensive disulfide bonding contributes to the insolubility of keratins, except in dissociating or reducing agents such as urea.

[edit] Keratin and hair protein biochemistry

Evidence is given for the progress in hair keratin research by bringing out four examples from the recent hair science literature. 1 Kon et al. [ 1] published a new method of solubilization and fractionation of the matrix and the microfibril proteins and found a significant decrease in the ‘intact’ microfibril keratin at the tip end of permed hair. 2 Contrary to the previous view of the existence of four major and one minor hair keratin pair, Langbein et al. [ 2, 3] showed that there are nine type I hair keratins and six type II hair keratins and drew up a two-dimensional catalogue of human hair keratins. 3 To collectively describe the extremely complex expression pattern of human type I and type II hair keratins in the hair follicle, Langbein et al. [ 2, 3] have summarized the corresponding RNA expression profiles of the various hair keratins schematically. 4 Contrary to the previous assignment of keratins exclusively to the microfibrils in the cortex, the mRNA expression studies of Langbein et al. [ 2, 3] implied that any hair cuticle cell leaving the living cell compartment contains four different hair keratins. The more flexible and elastic keratins of hair have fewer interchain disulfide bridges than the keratins in mammalian fingernails, hooves and claws (homologous structures), which are harder and more like their analogs in other vertebrate classes. Hair and other α-keratins consist of α-helically-coiled single protein strands (with regular intra-chain H-bonding), which are then further twisted into superhelical ropes that may be further coiled. The β-keratins of reptiles and birds have β-pleated sheets twisted together, then stabilized and hardened by disulfide bridges.

[edit] Silk

Silk found in insect pupae, and in spider webs and egg casings, also has twisted β-pleated sheets incorporated into fibers wound into larger supermolecular aggregates. The structure of the spinnerets on spiders’ tails, and the contributions of their interior glands, provide remarkable control of fast extrusion. Spider silk is typically about 1 to 2 micrometres (µm) thick, compared with about 60 µm for human hair, and more for some mammals. (Hair, or fur, occurs only in mammals.) The biologically and commercially useful properties of silk fibers depend on the organization of multiple adjacent protein chains into hard, crystalline regions of varying size, alternating with flexible, amorphous regions where the chains are randomly coiled.[1] A somewhat analogous situation occurs with synthetic polymers such as nylon, developed as a silk substitute. Silk from the hornet cocoon contains doublets about 10 µm across, with cores and coating, and may be arranged in up to 10 layers; also in plaques of variable shape. Adult hornets also use silk as a glue, as do spiders.

[edit] List of human tissues containing keratin

• Hair
• Nails
• Skin

[edit] Diseases caused by mutations in the keratin genes

• Epidermolysis bullosa simplex
• Ichthyosis bullosa of Siemens
• Epidermolytic hyperkeratosis

[edit] See also

• Acne
• Keratosis pilaris
• Intermediate filament
• Desmosome
• Keratin 1
• Keratin 10

[edit] References

• World Book Encyclopedia (1998)

[edit] External links

• Composition and β-sheet structure of silk
• Spider silk fiber structure
• Hair-Science.com's entry on the miroscopic elements of hair