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Prefoldin is a family of proteins used in protein folding complexes. It is classified as a heterohexameric molecular chaperone in both archaea and eukarya, including humans. A prefoldin molecule works as a transfer protein in conjunction with a molecule of chaperonin to form a chaperone complex and correctly fold other nascent proteins. One of prefoldin's main uses in eukarya is the formation of molecules of actin for use in the eukaryotic cytoskeleton. ==Purpose and Uses== Prefoldin is one family of chaperone proteins found in the domains of eukarya and archaea. Prefoldin acts in combination with other molecules to promote protein folding in cells where there are many other competing pathways for folding.〔“Oxford Dictionary of Biochemistry and Molecular Biology.” Oxford University Press, Oxford, 1997.〕 Chaperone proteins perform non-covalent assembly of other polypeptide-containing structures ''in vivo''. They are implicated in the folding of most other proteins. In archaea, prefoldins are believed to function in combination with group II chaperonins〔Clark, D. S., Whitehead, T.A., ''et al.''. (2007). A filamentous molecular chaperone of the prefoldin family from the deep-sea hyperthermophile ''Methanocaldococcus jannaschii''. ''Protein Science'', 16:626–634.〕 in ''de novo'' protein folding. In eukarya however, prefoldins have acquired a more specific function: they are used to establish correct tubular assembly for many tubular proteins, such as actin.〔Cowan, N. J., Vainberg, I.E., Lewis, S.A., ''et al.''. (1998). Prefoldin, a Chaperone that Delivers Unfolded Proteins to Cytosolic Chaperonin. ''Cell'', Vol. 93:863–873.〕 Actin accounts for 5-10% of all protein found in eukaryotic cells, which therefore means that prefoldin is quite prevalent in the cells. Actin is made of two strings of beads wound round each other and is one of the three main parts of the cytoskeleton of eukaryotic cells.〔Fruton, Joseph S.: “Protein, Enzymes, Genes; The interplay of chemistry and Biology.” Yale University Press, New Haven, 1999.〕 Prefoldin bonds specifically to cytosolic chaperonin protein. This complex of prefoldin and chaperonin then forms molecules of actin in the cytosol. The prefoldin acts as a transporter molecule that transports bound, unfolded target proteins to the chaperonin (C-CPN) molecule.〔 For example, the prefoldin that is used in the formation of actin also transfers α or β tubulin to a cytosolic chaperonin. The prefoldin, however, does not form a ternary complex with tubulin and chaperonin. Once the tubulins are in contact with the chaperonin, the prefoldin automatically lets go and leaves the active site, due to its high affinity for the chaperonin molecule. Once the prefoldin is in contact with the chaperonin protein, it loses its affinity for the unfolded target protein. Prefoldin is triggered only to bind to nonnative target proteins in the cytosol so that it will only bind to unfolded proteins. Unlike many other molecular chaperones, prefoldin does not use chemical energy, in the form of adenosine triphosphate (ATP), to promote protein folding.〔Pockley, A.: “Molecular Chaperones and Cell Signaling.” Cambridge University Press, Cambridge, 2005.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Prefoldin」の詳細全文を読む スポンサード リンク
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