Chaperonin-facilitated protein folding

D. Engineering Disulfide Bonds in Bamase VII. Chaperonin-Facilitated Protein Folding... 

M. J. Todd, G. H. Lorimer, and D. Thirumalai, Chaperonin-facilitated protein folding Optimization of rate and yield by an iterative annealing mechanism. Proc. Natl. Acad. Sci. 

Tian, G., I. E. Vainberg, W. D. Tap, S. A. Lewis, and N. J. Cowan (1995a). Quasi-native chaperonin-bound intermediates in facilitated protein folding. J. Biol. Chem. 270, 23910-23913. 

The eukaryotic chaperonin TRiC (T-complex polypeptide (TCP-1) ring complex or cytosolic chaperonin-containing TCP-1 (CCT)) is composed of an eight-subunit Hsp60 complex. The barrel-shaped TRiC complex binds to partially folded or misfolded target proteins and holds the protein to facilitate protein folding. The TRiC chaperonin is required for the folding of proteins such as tubulin, actin, and a number of other structurally complex proteins. 

Some imported proteins can fold into their final, active conformation without further assistance. Final folding of many matrix proteins, however, requires a chaperonin. As discussed in Chapter 3, chaperonin proteins actively facilitate protein folding in a process that depends on ATP. For instance, yeast mutants defective in HscGO, a chaperonin in the mitochondrial matrix, can Import matrix proteins and cleave their uptake-targeting sequence normally, but the imported polypeptides fall to fold and assemble into the native tertiary and quaternary structures. 

Chaperonins are huge macromolecular assemblies whose function is to facilitate protein folding proteins enter into a cavity present in the chaperonin, in which they can fold in the absence of any perturbation from the environment. Not all the proteins in a cell require the assistance of chaperonins in bacteria, only 5% of the proteins require chaperonins for their proper folding. What distinguishes the two classes of proteins, those that need chaperonins and those that can fold by themselves An answer in terms of different physicochemical characteristics of the two classes of proteins, has been actively sought. Interesting observations have been made, suggesting that some structural families of proteins are more dependent on... 

The Rieske protein II (SoxF) from Sulfolobus acidocaldarius, which is part, not of a bci or b f complex, but of the SoxM oxidase complex 18), could be expressed in E. coli, both in a full-length form containing the membrane anchor and in truncated water-soluble forms 111). In contrast to the results reported for the Rieske protein from Rhodobacter sphaeroides, the Rieske cluster was more efficiently inserted into the truncated soluble forms of the protein. Incorporation of the cluster was increased threefold when the E. coli cells were subject to a heat shock (42°C for 30 min) before induction of the expression of the Rieske protein, indicating that chaperonins facilitate the correct folding of the soluble form of SoxF. The iron content of the purified soluble SoxF variant was calculated as 1.5 mol Fe/mol protein the cluster showed g values very close to those observed in the SoxM complex and a redox potential of E° = +375 mV 111). 

For many proteins, folding is facilitated by Hsp70 chaperones and by chaperonins. 

Chaperonins, which directly facilitate the folding of proteins... 

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