A Thermodynamic Coupling Mechanism for the Disaggregation of a Model Peptide Substrate by Chaperone SecB

Panse, Vikram G and Vogel, Pia and Trommer, Wolfgang E and Varadarajan, Raghavan (2000) A Thermodynamic Coupling Mechanism for the Disaggregation of a Model Peptide Substrate by Chaperone SecB. In: Journal of Biological Chemistry, 275 (25). pp. 18698-18703.

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Abstract

Molecular chaperones prevent protein aggregation in vivo and in vitro. In a few cases, multichaperone systems are capable of dissociating aggregated state(s) of substrate proteins, although little is known of the mechanism of the process. SecB is a cytosolic chaperone, which forms part of the precursor protein translocation machinery in Escherichia coli. We have investigated the interaction of the B-chain of insulin with chaperone SecB by light scattering, pyrene excimer fluorescence, and electron spin resonance spectroscopy. We show that SecB prevents aggregation of the B-chain of insulin. We show that SecB is capable of dissociating soluble B-chain aggregates as monitored by pyrene fluorescence spectroscopy. The kinetics of dissociation of the B-chain aggregate by SecB has been investigated to understand the mechanism of dissociation. The data suggests that SecB does not act as a catalyst in dissociation of the aggregate to individual B-chains, rather it binds the small population of free B-chains with high affinity, thereby shifting the equilibrium from the ensemble of the aggregate toward the individual B-chains. Thus SecB can rescue aggregated, partially folded/misfolded states of target proteins by a thermodynamic coupling mechanism when the free energy of binding to SecB is greater than the stability of the aggregate. Pyrene excimer fluorescence and ESR methods have been used to gain insights on the bound state conformation of the B-chain to chaperone SecB. The data suggests that the B-chain is bound to SecB in a flexible extended state in a hydrophobic cleft on SecB and that the binding site accommodates approximately 10 residues of substrate.

Item Type:	Journal Article
Publication:	Journal of Biological Chemistry
Publisher:	American Society for Biochemistry and Molecular Biology
Additional Information:	Copyright of this article belongs to American Society for Biochemistry and Molecular Biology
Keywords:	Biochemistry;Molecular Biophysics;Methods and Techniques
Department/Centre:	Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited:	17 Oct 2007
Last Modified:	29 Sep 2010 09:09
URI:	http://eprints.iisc.ac.in/id/eprint/12103

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