Native-Like Structure of a Protein-Folding Intermediate Bound to the Chaperonin GroEL

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 94; no. 4; pp. 1080 - 1085
• Main Authors: Goldberg, Matthew S., Zhang, Jing, Sondek, Stacey, Matthews, C. Robert, Fox, Robert O., Horwich, Arthur L.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 18.02.1997; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences of the USA
• Subjects: Amides; Amides - chemistry; Bacteria; Biochemistry; Biological Sciences; Chaperonin 60 - genetics; Chaperonin 60 - metabolism; Deuterium; Escherichia coli; Exchange rates; Flow Injection Analysis - methods; Fluorescence; Humans; Hydrogen bonds; Kinetics; Magnetic Resonance Spectroscopy; Models, Molecular; Potassium phosphates; Protein Conformation; Protein Denaturation; Protein Folding; Protein refolding; Proteins; Protons; Recombinant Proteins - metabolism; Spectroscopy; Tetrahydrofolate Dehydrogenase - genetics; Tetrahydrofolate Dehydrogenase - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.94.4.1080

The chaperonin GroEL binds nonnative proteins in its central channel through hydrophobic interactions and initiates productive folding in this space underneath bound cochaperone, GroES, in the presence of ATP. The questions of where along the folding pathway a protein is recognized by GroEL, and how much structure is present in a bound substrate have remained subjects of discussion, with some experiments suggesting that bound forms are fully unfolded and others suggesting that bound species are partially structured. Here we have studied a substrate protein, human dihydrofolate reductase (DHFR), observing in stopped-flow fluorescence experiments that it can rapidly bind to GroEL at various stages of folding. We have also analyzed the structure of the GroEL-bound protein using hydrogen-deuterium exchange and NMR spectroscopy. The pattern and magnitude of amide proton protection indicate that the central parallel β -sheet found in native DHFR is present in a moderately stable state in GroEL-bound DHFR. Considering that the β -strands are derived from distant parts of the primary structure, this suggests that a native-like global topology is also present. We conclude that significant native-like structure is present in protein-folding intermediates bound to GroEL.