PROTEIN FOLDING IN THE EUKARYOTIC CYTOSOL

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DESCRIPTION: Chaperonins are ubiquitous multisubunit toroidal ATPases that faciliate protein folding. In the eukaryotic cytosol, cytosolic caperonin (c-cpn) is required for the faciliated folding of actins and tubulins. The PI has discovered five protein cofactors (termed A-E) that act on c-cpn-generated folding intermediates and are required for the formation of native a- and b- tubulin in vitro. 1) They will use combined biochemical, cell biological and genetic approaches to test the interrelated hypotheses i)that in the tubulin heterodimer, a- and b- tubulin polypeptides do not exist in a thermodynamically minimal energy state, and that the function of cofactors is to form and maintain this activated state, and ii) that the cascade of cofactor interactions leading from unfolded to native a- and b- tubulin converge, because each subunit requires the other in order to fold properly. 2)They will obtain structural data on the cofactors. 3) They will investigate the functional significance of the observation that three of the tubulin folding confactors behave as MAPs by a) examining their microtubule binding probperties in vitro and in vivo, and b) establishing their potential regulatory role in tubulin synthesis. 4) They will characterize a newly discovered activity that enhances c-cpn efficiency. 5) They have shown that only c-cpn (and not its prokaryotic or mitochondrial homologs) can facilitate the productive folding of actins and tubulins. They therefore propose to test the hypotheis that chaperonins other than c-cpn have a restricted target range by examining the abitlity of c-cpn, the mitochondrial chaperonin Hsp60/Hsp10, and the prokaryotic chaperonin GroEL/GroES to substitute for one another in vitro and in vivo.