On the Role of Symmetrical and Asymmetrical Chaperonin Complexes in Assisted Protein Folding
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M. K. Hayer-Hartl
Abstract
The cylindrical chaperonin GroEL of E. coli and its ring-shaped cofactor GroES cooperate in mediating the ATP-dependent folding of a wide range of polypeptides in vivo and in vitro. By binding to the ends of the GroEL cylinder, GroES displaces GroEL-bound polypeptide into an enclosed folding cage, thereby preventing protein aggregation during folding. The dynamic interaction of GroEL and GroES is regulated by the GroEL ATPase and involves the formation of asymmetrical GroEL:GroES1 and symmetrical GroEL: GroES2 complexes. The proposed role of the symmetrical complex as a catalytic intermediate of the chaperonin mechanism has been controversial. It has also been suggested that the formation of GroEL:GroES2 complexes allows the folding of two polypeptide molecules per GroEL reaction cycle, one in each ring of GroEL. By making use of a procedure to stabilize chaperonin complexes by rapid crosslinking for subsequent analysis by native PAGE, we have quantified the occurrence of GroEL:GroES1 and GroEL:Groesr2 complexes in active refolding reactions under a variety of conditions using mitochondrial malate dehydrogenase (mMDH) as a substrate. Our results show that the symmetrical complexes are neither required for chaperonin function nor does their presence significantly increase the rate of mMDH refolding. In contrast, chaperonin-assisted folding is strictly dependent on the formation of asymmetrical GroEL:Groes1 complexes. These findings support the view that GroEL:Groes2 complexes have no essential role in the chaperonin mechanism.
Copyright ©1999 by Walter de Gruyter GmbH & Co. KG
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Articles in the same Issue
- Biosynthesis of Glycosylphosphatidylinositols in Mammals and Unicellular Microbes
- Activation of DNA Replication in Yeast by Recruitment of the RNA Polymerase II Transcription Complex
- On the Role of Symmetrical and Asymmetrical Chaperonin Complexes in Assisted Protein Folding
- Regulation of Cathepsin B Activity by Cysteine and Related Thiols
- Epitope Mapping of the Monoclonal Antibody MM12.10 to External MDR1 P-Glycoprotein Domain by Synthetic Peptide Scanning and Phage Display Technologies
- Molecular Mimicry between a Monoclonal Antibody and One Subunit of Crotoxin, a Heterodimeric Phospholipase A2 Neurotoxin
- Enzyme-Linked Immunosorbent Assay for the Measurement of JNK Activity in Cell Extracts
- Mitochondrial DNA Acts as Potential Promoter of the Baculovirus RNA Polymerase
- In Vitro Phosphorylation of Purified Glycosylphos-phatidylinositol-Specific Phospholipase D
- Cathepsin S and Cruzipain Are Inhibited by Equistatin from Actinia equina
- Lipopeptides as Dimerization Inhibitors of HIV-1 Protease
