Fibrous proteins, /?-structures characteristics

Amyloid deposits are fibrous protein structures of high P-sheet content that are identified microscopically from their staining characteristics, giving a green birefringence when stained with the dye Congo red. 

Hydrogen Bonds. Many characteristics of H bonds have already been discussed because of the major role they play in stabilizing fibrous proteins. Additional aspects of H bonds to be considered relate more closely to the structures of globular proteins. Evidence for the existence of an H bond comes from the observation of a decreased distance between donor and acceptor groups forming the H bond. 

Keratins are insoluble proteins that make up such structures as hair, skin, nails, wool, and feathers and form the cytoskeleton structures in all cells of epithelial origin. Along with other fibrous proteins of the same dimensions (e.g., neurofilaments), keratin has been referred to as intermediary filament (IF). In the human being, keratin is one of the more abundant proteins. The basic keratin unit is a relatively small protein with a molecular weight of 40,000-70,000. About 20 different keratin polypeptides have been identified in human hair follicles, various epithelial cells, and tumor cells. They have been assigned numbers 1-20 and have been divided into two classes acidic (type 1) and neutral/base (type 2). A given tissue or cell line will have a characteristic keratin polypeptide distribution, as shown in Table 8.2. However, both types of peptides are always present in a given cell. 

In 1951, Pauling and Corey published a landmark paper on the structure of polypeptide chains. Earlier X-ray diffraction work in the 1930s had revealed the characteristics of the peptide bond and studies of fibrous proteins suggested that helical and extended chain structures were probably present. Using... 

Clarifying the structure and functions of protein materials in the solid state provides an index with respect to the design of artificial biomaterials. Solid-state NMR has been used as a powerful means for elucidating structure and dynamics in addition to the X-ray diffraction method [le]. The structure and dynamics of some fibrous proteins, such as wool, silk, collagen, tropomyosin, etc., have been characterized using characteristic solid-state NMR chemical shifts as stated above, and much more new information obtained in addition to the results provided by X-ray diffraction. And the individual advantages of these two methods are complementary with each other. Details of appli-... 

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). 

Proteins typically have either globular or fibrous tertiary structures. These tertiary structures do not occur randomly. Under the proper environmental conditions the tertiary structure of a protein occurs in one particular way—a way that is characteristic of that particular protein and one that is often highly important to its function. 

What secondary and tertiary structures are characteristic of fibrous proteins ... 

A j8-structure, necessarily antiparallel, may also be formed within a single chain, when it doubles on itself to form a hairpin or, if the chain is long enough, two remote parts of the sequence may also be able to unite in a parallel ]3-structure. The a-helix and the j8-sheet (to which one may add the special configuration of the chain that allows it to make the hairpin bend, and very rare bits of freak helices seen in some proteins) define the secondary structure of the protein. The key to protein structure was the recognition that it is uniquely determined by the amino acid sequence— the primary structure— alone. Some sequences define fibrous, and others (the majority) globular proteins, and we will now consider their characteristics and functions. 

Secondary structure refers to the repeating patterns in the arrangement of protein chains. These are maintained by interactions between the peptide backbones of amino acids that are close together in the chain sequence or adjacent to each other on neighboring chains. Secondary structure is characteristic of fibrous proteins, but globular proteins also frequently feature regions of a-helix, j8-pleated sheet, and random coil secondary structure. 

Muscle is a complex assembly of proteins embracing the metabolic capabilities characteristic of globular proteins and the structural capabilities of fibrous proteins and is thus well suited to perform the dual roles of converting chemical energy into mechanical energy and sustaining tension. Over 40 years ago a combination of electron microscopy and X-ray fibre... 

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