Polypeptides, GroEL

Another intriguing facet of polypeptide-GroEL interaction is the effect of binding on the structure of the non-native substrate. It is conceivable that the chaperonin, like other cellular chaperones, is a passive... 

GroEL is a cylindrical structure with a central channel in which newly synthesized polypeptides bind... 

Figure 6.12 (a) Schematic diagram of one subunit of GroEL. The polypeptide chain is folded info three domains. The equatorial domain (green) is the largest domain, comprising 10 a helices, and is built up from both the N-tetminal and the C-terminal regions. 

The GroEL-GroES complex binds and releases newly synthesized polypeptides in an ATP-dependent cycle... 

Fenton, W.A., et al. Residues in chaperonin GroEL required for polypeptide binding and release. 

A polypeptide consisting of residues 191-345 of GroEL that, when immobilized on agarose, acts as a very efficient chaperone with proteins that resist renaturation by conventional refolding methods. Immobilized minichap-... 

Within the GroEL-GroES cage polypeptide chains can fold without becoming entangled with other proteins or being cleaved by protein-hydrolyzing enzymes... 

Many of the chaperones double as heat shock-proteins (Hsp). When a cell is put under stress that can cause proteins to denature, such as too high a temperature, it produces heat-shock proteins. Their names are abbreviated to Hsp plus their subunit molecular mass in kDa. Hsp70, for example, is a ubiquitous heat-shock protein in eukaryotes. It is known in E. coli as DnaK for historical reasons because it was first discovered from a supposed role in DNA replication. Hsp70 is also important in protein trafficking and the conveying of proteins across membranes, because the denatured state is important in these processes. In protein biosynthesis, the unfolded state of the nascent polypeptide chain is passed on to DnaK, which maintains it in an extended form. The chain, under the influence of ATP and co-chaperones such as DnaJ and GrpE, is handed over to GroEL. 

Landry, S.J., Jordan, R., McMacken, R., and Gierasch, L. M. (1992). Different conformations for the same polypeptide bound to chaperones DnaK and GroEL. Nature (London) 355, 455-457. 

Figure 2 Mechanism of action of the GroEL/GroES system in E.coli. P, unfolded polypeptide chain. N, native folded chain. For details, see text. Reprinted from Reference (16), Copyright 2003 with permission from Elsevier.

Expanded GroEL-GroES complex with enclosed folding polypeptide"... 

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