Scleroprotein

(biochemistry) Any of a class of highly insoluble proteins representing the principal structural elements of many animal tissues.

One of two major classes of protein molecules, the other being termed globular protein. Fibrous proteins function either in a filamentous aggregate or as long, thin molecules.

One major category of fibrous proteins is the α-fibrous group. It includes intermediate filaments (occurring in skin, wool, and neurons), muscle proteins (myosin, paramyosin, and tropomyosin), and fibrinogen (a plasma protein that forms clots). The protein chain forms a right-handed α-helical structure that is stabilized by hydrogen bonds that lie parallel to the axis of the helix (see illustration). Non-filament-forming α-fibrous proteins include laminin, a triple-stranded molecule found in the basement membrane of certain cells.

Fibrous proteins. (a) α-Fibrous protein. (b) Collagen.

The second major category is based on the β structure. Feather and scale keratin have a twisted β-sheet structure, that is, an extended array of chains which are held together by hydrogen bonds positioned perpendicular to the chain axis. The sheet aggregates laterally and helically to generate a filamentous structure.

The third major category is exemplified by collagen, a major component of skin, tendon, bone, cornea and cartilage (see illustration). The molecules contain three chains, each of which coils up into a threefold helix. The chains then coil around one another in a right-handed manner to generate the collagen molecule. In turn, molecules generally aggregate to form fibrils.

Fibrous proteins also include the thin filaments of muscle in which globular subunits aggregate helically, and individual molecules that contain long strings of globular domains. See also Collagen; Fibrinogen; Muscle proteins; Protein.

Tropocollagen triple helix.

Scleroproteins are one of the two main classes of protein Quaternary structure (the other being globular proteins).

They are also called fibrous proteins.

Contents 1 Characteristics 2 Functions 3 Examples 4 See also 5 References 6 External links

Characteristics

They form long protein filaments, rod- or wire-like shapes. They are usually inert structural or storage proteins. They are generally water-insoluble and are found as an aggregate due to hydrophobic R groups that stick out of the molecule. The amino acid sequences they are made from often have limited residues with repeats. These can form unusual secondary structures, e.g. collagen triple helix. The structures often contain 'cross-links' between chains, for example cys-cys disulfide bonds between keratin chains.

Globular proteins tend to denature more easily than fibrous proteins.

Functions

They usually play a role which is protective or supportive.^[1]

They are usually used to construct connective tissues, tendons, bone matrix and muscle fiber.

Attempts at artificial synthesis have been made.^[2]

Examples

Examples of include keratins, collagens and elastins.

Another example is fibroin.^[3]

See also

• Wikipedia:MeSH_D12.776#MeSH_D12.776.860_---_scleroproteins

References

1. ^ scleroprotein at Dorland's Medical Dictionary
2. ^ Miroshnikov KA, Marusich EI, Cerritelli ME, et al. (April 1998). "Engineering trimeric fibrous proteins based on bacteriophage T4 adhesins". Protein Eng. 11 (4): 329–32. PMID 9680195. http://peds.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=9680195. 
3. ^ "Fibrous Protein Homepage". http://web.chemistry.gatech.edu/~williams/bCourse_Information/6521/protein/fibrous/fibrous.html. Retrieved 2008-11-26. 

External links

• MeSH Scleroproteins

v • d • e Proteins Processes Protein biosynthesis - Posttranslational modification - Protein folding - Protein targeting - Proteome - Protein methods Structures Protein structure - Protein structural domains - Proteasome Types List of types of proteins - List of proteins - Membrane protein - Globular protein (Globulin, Albumin) - Fibrous protein

v • d • e Protein: scleroproteins Extracellular matrix Collagen 1-12 type I (COL1A1, COL1A2) · type II (COL2A1) · type III · type IV (COL4A1, COL4A2, COL4A3, COL4A4, COL4A5, COL4A6) · type V (COL5A1, COL5A2, COL5A3) · type VI (COL6A1, COL6A2, COL6A3) · type VII (COL7A1) · type VIII (COL8A1, COL8A2) · type IX (COL9A1, COL9A2, COL9A3) · type X (COL10A1) · type XI (COL11A1, COL11A2) · type XII (COL12A1) 13-29 COL13A1 · COL14A1 · COL15A1 · COL16A1 · COL17A1 · type XVIII (COL18A1, Endostatin) · COL19A1 · COL20A1 · COL21A1 · COL22A1 · COL23A1 · COL24A1 · COL25A1 · COL26A1 · COL27A1 · COL28A1 · COL29A1 Enzymes Prolyl hydroxylase/Lysyl hydroxylase · Cartilage associated protein/Leprecan · ADAMTS2 · Procollagen peptidase · Lysyl oxidase Tenascin Tenascin C · Tenascin X Laminin alpha (LAMA1, LAMA2, LAMA3, LAMA4, LAMA5) · beta (LAMB1, LAMB2, LAMB3, LAMB4) · gamma (LAMC1, LAMC2, LAMC3) Other ALCAM · Elastin (Tropoelastin) · Vitronectin Keratin/Cytokeratin Epithelial keratins (soft alpha-keratins) type I/chromosome 17 (10, 12, 13, 14, 15, 16, 17, 19, 20) · chromosome 12 (18) · none (21) type II/chromosome 12 (1, 2A, 3, 4, 5, 6A, 6B, 7, 8, 9) Hair keratins (hard alpha-keratins) type I/chromosome 17 (31, 32, 33A, 33B, 34, 35, 36, 37, 38) type II/chromosome 12 (81, 82, 83, 84, 85, 86) Ungrouped alpha chromosome 17 (23, 24, 25, 26, 27, 28, 39, 40) chromosome 12 (71, 72, 73, 74, 75, 76, 77, 78, 79, 80) Not alpha Beta-keratin Other Gelatin · Reticulin see also diseases

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