Hair keratin

by Séverine Altairac

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Hair is found in all shapes, sizes and texture. It can be curly, straight or wavy, easy to deal with or just downright impossible. And whatever hair is like, hairdressers can modify and sculpt it – within reason – to satisfy a person’s fantasy. On the whole, hair is docile. And its docility is mostly due to the structure of keratin, a large family of proteins.

Hair starts growing from a bulb which is lodged just under the skin. The beginning of a hair is made up of cells, which are bulging with keratin. The cells lengthen and then die, leaving behind protein bundles. There are two types of keratin: I and II. And their intertwining form long coils which accumulate in hair.

Hair structure depends on chemical bonds between keratins, which interact by way of hydrogen molecules – and bonds such as these are easily broken by water, or even humidity. When hair dries, the bonds reform, stabilizing the hair as it is. Which would explain some of the architectural tragedies which occur to hair in humid weather. Blow-drying, on the other hand, has the power of reorganizing all these bonds and can sculpt hair until the next rainfall.

Besides hydrogen bonds, keratin can also establish other more stable bonds with its neighbors, thanks to cysteine which form disulfide bonds. Disulfide bonds are far more stable than hydrogen bonds, and molecules other than water are needed to break them. And once broken, the keratin bundles can be tamed, and hairdressers can modify their natural state by either curling them, or straightening them. The reason why some of us are born with curly hair and others with straight hair, all has to do with the hair bulb – and not keratin. A cylindrical bulb will form round – and hence straight – hair, whilst an oval bulb will produce flat – and hence curly – hair.

Though hairstyles are short-lived, hair is not. Hair is a tissue that can last for thousands of years and because of this, historians now know that Pharaoh Ramses II was a red head, for instance. What is more, hair is not only a choice tissue on a crime scene to help identify either a victim or the offender but can also betray many things, such as eating habits, drug abuse or poisoning. Some truths are but a whisker away…

UniProt cross references
Keratin, type I cuticular Ha1, Homo sapiens (human): Q15323
Keratin, type I cuticular Ha2, Homo sapiens (human): Q14532
Keratin, type I cuticular Ha4, Homo sapiens (human): O76011
Keratin, type I cuticular Ha5, Homo sapiens (human): Q92764
Keratin, type I cuticular Ha6, Homo sapiens (human): O76013
Keratin, type I cuticular Ha7, Homo sapiens (human): O76014
Keratin, type I cuticular Ha8, Homo sapiens (human): O76015
Keratin, type I cuticular Ha3-I, Homo sapiens (human): O76009
Keratin, type I cuticular Ha3-II, Homo sapiens (human): Q14525
Keratin, type II cuticular Hb1, Homo sapiens (human): Q14533
Keratin, type II cuticular Hb2, Homo sapiens (human): Q9NSB4
Keratin, type II cuticular Hb3, Homo sapiens (human): P78385
Keratin, type II cuticular Hb4, Homo sapiens (human): Q9NSB2
Keratin, type II cuticular Hb5, Homo sapiens (human): P78386
Keratin, type II cuticular Hb6, Homo sapiens (human): O43790
Protein Spotlight (ISSN 1424-4721) is a monthly review written by the Swiss-Prot team of the SIB Swiss Institute of Bioinformatics. Spotlight articles describe a specific protein or family of proteins on an informal tone. Follow us: Subscribe · Twitter · Facebook