Keratins alpha

Human hair is made of protofibrils, which are twisted bundles of the coiled protein alpha-keratin. Alpha-keratin is so strong and flexible that a human hair can be tied in a knot without breaking. 

Bocker W, Bier B, Ereytag G, Brommelkamp B, et al. An immunohistochemical smdy of the breast using antibodies to basal and luminal keratins, alpha-smooth muscle actin, vimentin, collagen IV and laminin. Part II Epitheliosis and ductal carcinoma in sim. Virchows Arch A Pathol Anat Histopathol. 1992 421 323-330. 

Alpha helices are sufficiently versatile to produce many very different classes of structures. In membrane-bound proteins, the regions inside the membranes are frequently a helices whose surfaces are covered by hydrophobic side chains suitable for the hydrophobic environment inside the membranes. Membrane-bound proteins are described in Chapter 12. Alpha helices are also frequently used to produce structural and motile proteins with various different properties and functions. These can be typical fibrous proteins such as keratin, which is present in skin, hair, and feathers, or parts of the cellular machinery such as fibrinogen or the muscle proteins myosin and dystrophin. These a-helical proteins will be discussed in Chapter 14. 

Alpha farnesene, structure of, 207 Alpha helix (protein), 1038 Alpha-keratin, molecular model of, 1039... 

Van Scott EJ, Yu RJ (1974) Control of keratinization with alpha-hydroxy acids and related compounds. I. Topical treatment of ichthyotic disorders. Arch Dermatol no 586-590... 

It is a lipophilic compound which removes intercellular lipids that are covalently linked to the cornified envelope surrounding epithelial cells [3]. It also enhances penetration of other agents. Resorcinol (m-dihydroxy benzene) is structurally and chemically similar to phenol. It disrupts the weak hydrogen bonds of keratin [4]. Lactic acid is an alpha hydroxy acid which causes corneocyte detachment and subsequent desquamation of the stratum corneum [5]. 

Keratins are alpha-type fibrous polypeptides with a diameter of 7 11 nm. They are important components of the cytoskeleton in almost all epithelial cells as well as in some nonepithelial cell types. Keratins are generally held to be the most ubiquitous markers of epithelial differentiation. So far, 20 distinct types numbered by Moll et al. (1982a, 1990, 1992) have been revealed. Keratins were earlier thought to be separable into hard and soft, or cytokeratins and other keratins, but these designations are now understood to be incorrect. In 2006, a new nomenclature (Schweizer et al. 2006) was adopted for describing keratins which takes this into account (Table 13.1). 

This section summarizes the current information about different human keratins, their functional significance, cell-type-specific distribution as well as their coexpression with myoepithelial markers and estrogen receptor alpha (ER), because these markers exhibit characteristic expression patterns in some human breast tumors. In many of these cases, a definite diagnosis can be achieved only when additional information is provided by immunohistochemistry. 

As regards malignant tumors, K8 and K18 (and also K7 and K19) are expressed in most breast carcinomas (breast carcinomas of luminal phenotype luminal-type breast carcinomas) as the only keratins. Most of these tumors express estrogen receptor alpha and comprise about 90% of all cases of breast cancer most breast carcinomas therefore constitutively express the classical glandular keratins K7, K8,... 

FIGURE 10.4 Alpha-keratin helix for the copolymer derived from glycine and leucine. 

Secondary bonding is involved in forming the helical structures allowing the various bundles of alpha-keratin to be connected by weak secondary interactions, which in turn allow them to readily slide past one another. This sliding or slippage along with the... 

Our fingernails are also composed of alpha-keratin, but keratin with a greater amount of sulfur cross-links giving a more rigid material. In general, for both synthetic and natural polymers, increased cross-linking leads to increased rigidity. 

Santos, M., Perez, P., Segrelles, C., Ruiz, S., Jorcano, J. L., and Paramio, J. M. (2003). Impaired NF-kappa B activation and increased production of tumor necrosis factor alpha in transgenic mice expressing keratin K10 in the basal layer of the epidermis. J. Biol. Chem. 278, 13422-13430. 

Fibrous proteins also gain strength due to interactions between the side chains of the residues. The alpha-keratin polypeptides, for example, have a large number of cystine residues, which can form disulfide bonds. 

Coils such as those found in alpha-keratin are not the only structural motifs present in fibrous proteins. Silk, for example, is largely composed of fibrous proteins whose structures resemble interleaved sheets, see also Quaternary Structure Secondary Structure Tertiary Structure. 

Biological macromolecules are often distinguished by their helical structures to which one-dimensional space-group symmetries are applicable. Figure 8-15a shows Linus Pauling s sketch of a polypeptide chain, which he drew while he was looking for the structure of alpha-keratin. When he decided to fold the paper, he arrived at the alpha-helix. The solution may have come in a sudden moment,... 

Keratin Structure and Orientation. Acute flattening of the flbrous protein-fllled cells in the flnal stages of keratinization establishes a biaxial orientation. As would be expected, no birefrigence is observed normal to the plane of the comeum surface, but significant birefrigence is observed parallel to the plane of the corneum surface (I, 42). The x-ray diflFraction pattern of this isolated epidermal protein, when highly drawn, exhibits the classical alpha pattern (7, 43). 

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