Mammalian keratins

Schweizer J, Bowden PE, Coulombe PA, Langbein L, Lane EB, Magin TM, Maltais L, Omary MB, Parry DA, Rogers MA, Wright MW (2006) New consensus nomenclature for mammalian keratins. J Cell Biol 174(2) 169 174... 

William Thomas Astbury found that fibrous proteins, such as keratin, could behave as if they had more than one structure. Mammalian keratin, such as wool, normally gives a diffraction pattern referred to as the a-keratin X-ray pattern with repeat distances of 5.1 A. On stretching, however, a different diflfraction pattern, the y9-keratin pattern, is obtained. He found that it is possible to reconvert /3-keratin (stretched)... 

A third family of hard keratin proteins has been recognized by Gillespie [202]. In early studies, these proteins coprecipitated with low-sulfur proteins [203,204] but were found to represent a distinct family of proteins rich in aromatic residues (tyrosine and phenylalanine), glycine, and serine. These so-called high-tyrosine proteins consisted of two distinct classes, and their proportions varied widely in mammalian keratins (1-30% of total extracts) [205]. Apparently, high-tyrosine proteins are absent in human hair [191]. 

Squier CA (1982) Zinc iodide-osmium staining of membrane-coating granules in keratinized and non-keratinized mammalian oral epithelium. Arch Oral Biol 27 377-382... 

Mammalian skin must be tough, water-resistant, self-renewing, and rapidly healing. The outer layers of cells or epidermis consist principally of keratinocytes, epithelial cells specialized for formation of keratin (Fig. 7-31). In the inner layer of the epidermis the basal stem cells divide, providing a constant outward flow of cells which become progressively flattened, dehydrated, and filled with keratin fibrils.3 The outer layers contain only dead cells which are finally sloughed or abraded from the surface. Human epidermis is completely renewed in about 28 days ... 

Marshall, R. C Orwin, D. F. G., and Gillespie, J. M. (1991). Structure and biochemistry of mammalian hard keratin. Electron Microscopy Research 4,47-83. 

In the past decade a number of physical techniques have been used to evaluate the unique barrier properties of mammalian skin [1]. This chapter deals with the use of another physical technique, fluorescence spectroscopy, to study the barrier properties of the human stratum corneum (SC), specifically with respect to the transport of ions and water. The SC is the outermost layer of the human epidermis and consists of keratinized epithelial cells (comeo-cytes), physically isolated from one another by extracellular lipids arranged in multiple lamellae [2]. Due to a high diffusive resistance, this extracellular SC lipid matrix is believed to form the major barrier to the transport of ions and water through the human skin [3-5]. The objective of the fluorescence studies described here is to understand how such extraordinary barrier properties are achieved. First the phenomenon of fluorescence is described, followed by an evaluation of the use of anthroyloxy fatty acid fluorescent probes to study the physical properties of solvents and phospholipid membranes. Finally, the technique is applied to the SC to study its diffusional barrier to iodide ions and water. 

Stratum corneum, the outermost layer of mammalian epidermis, functions physiologically as the principal diflFusion barrier to molecules penetrating the skin and as a protective physical barrier to mechanical insults at the skin surface. Data suggest that these functions are critically dependent on the specific morphological and macromolecular organization of the membrane mosaic (16, 17, 18, 19, 20). Thus, alterations of biophysical properties arise from environmental factors acting directly on the membrane or upon the keratinization process, and they affect... 

Wools and other similar mammalian hairs are largely composed of keratin proteins. However, unlike the other natural proteinaceous fibre, silk, wool is cellular in nature the fibres consist of relatively hard, flattened, overlapping cuticle cells, which surround the central cortical cells in some fibres, these may in turn surround a hollow medulla (Figure 23). 

All eukaryotes possess a cytoskeleton, and parasitic protozoa are no exception. Cytoskeletal structures, particularly microtubular elements, classically have been among the major features used in defining the taxonomic relationships of protozoa. The cytoskeleton of higher eukaryotes contains three major types of protein filaments intermediate filaments, actin filaments and microtubules. Intermediate filaments are composed of fibrous, overlapping proteins those found in mammalian cells (e.g. keratins and lamins) have not yet been studied in protozoa. 

In the early 1930 s Astbury and his collaborators defined the principal features of the molecular structure of essentially all mammalian hard keratins (4, 6). This work introduced the concept of the regularly folded a-protein chain. Within this scheme of things the hard keratins of birds and reptiles stood out, for they gave highly characteristic diffraction patterns which could only be interpreted in terms of a special type of 0 or nonfolded chain (5). Nevertheless, much of the epidermal protein in birds and reptiles has the same a-type structure as is always found in the case of mammalian epidermal tissue. The special interest of these observations was to reveal a widespread common type of molecular structure in the principal fibrous proteins of vertebrate epidermis. This common type is not quite universal because of the seeming mutation in the hard keratins of birds and reptiles, which defines the unique relationship of these groups at the molecular level (5, 50). 

The group of proteins commonly known as high-tyrosine proteins (Mr less than 10,000) vary widely in their distribution and relative proportions across the various mammalian fiber types and other keratins. These proteins range from virtual absence in Lincoln wool and human hair to about 30-40% in echidna quill [240]. 

After oral administration, griseofulvin is specifically localized in a patient s keratinized cells, namely the epidermis, hair, and nails, and is used to injure fungi parasitizing these tissues. Griseofulvin blocks fungal mitosis, causing multinucleate cells to be formed (Gull and Trinci, 1973) mammalian (and plant) cells suffer similarly, so the selectivity depends on the initial distribution. 

Nucleoproteins are difficult to extract from mammalian spermatozoa this is not surprising because the nucleus of mammalian spermatozoa is protected against mechanical damage by a special keratinous membrane. The nuclear protein, like keratin, is rich in sulfur, but it contains more arginine than regular keratin. Studies on disrupted bull sperm nuclei revealed that the arginine content of mammalian sperm is intermediate between that of protamine and that of histone. Whether protamines are in fact present in mammalian sperm is not known. Analysis of a protein hydrolysate obtained after extraction of bull sperm does, however, indicate that a basic protein, relatively rich in arginine, is present in mammalian sperm. 

The hydrophilic and biodegradable c-poly(glutamic acid) has been used to modify chitosan matrices, and the resulting cytocompatible composite biomaterial showed to be suitable for tissue engineering applications [56]. Another potential skin replacement blend has been prepared using chitosan and the cysteine-rich major structural fibrous protein keratin that supported fibroblast attachment and proliferation, demonstrating to be a good substrate for mammalian cell culture [137]. 

The main nitrogenous end products of protein metabolism are amino acids, ammonia, uric acid, and urea. Much has been written concerning the excretion of these substances by various animals and the relationship this bears to their evolution, habitat, and mode of reproduction. The excretion of guanine by spiders and trimethylamine oxide by marine teleosts are important exceptions. Guanine deposited in fish scales and pterines in butterfly pigments might also be regarded as excretory products if one were also to consider as such the keratin of mammalian hair. 

The more flexible and elastic keratins in hair have fewer inter-chain disulfide bridges than the keratins in mammalian fingernails, hooves and claws (homologous structures). 

It is impossible to establish who first used this compound in the treatment of pathological conditions of the skin since it is shrouded in folklore and lay medicine. Certainly the use of aged urine (concentrated by evaporation), was popular for the treatment of warts, bunions, chilblains, brittle nails and scaling of the skin and extended well into the middle 30 s of this century. This lay treatment seems explicable on the basis of present day knowledge of the fundamental effects of urea on the keratinized cell layer of mammalian skin. 

Basic proteins of the histone type, or of a type intermediate between histone and protamine, are usually found in various amounts in cell nuclei of immature fish testes, often together with a protamine. Similar basic proteins of the histone type, but not protamines, are reported to be present in mature sperm cell nuclei of several fish and marine animals such as codfish (Stedman and Stedman, 1951), halibut, shad, sea urchin (Arbacia lixula and Stronglocentrotus lividus) starfish (Astropecten auran-tiacus and Echinaster spositus) (Kossel and Staudt, 1926), octopus (Eledone cirrosa) and some shellfish (Palau and Subirana, 1967). The same is true for some land animals such as Drosophila [Das et aL, 1964 (1,2,3)], grasshopper (Bloch and Brack, 1964 Das et al. 1965), and cricket (Kaye and McMaster-Kaye, 1966). No basic proteins can be readily extracted from mammalian sperm nuclei by acids (Dallam and Thomas, 1953). Nevertheless, there appears to exist in mammalian semen a basic keratin-like protein containing cystine in combination with DNA in a molecular ratio... 

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