Journal of Biological Chemistry
Volume 278, Issue 49, 5 December 2003, Pages 48644-48650
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Protein Structure and Folding
The Selective Inhibition of Serpin Aggregation by the Molecular Chaperone, α-Crystallin, Indicates a Nucleation-dependent Specificity*

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Small heat shock proteins (sHsps) are a ubiquitous family of molecular chaperones that prevent the misfolding and aggregation of proteins. However, specific details about their substrate specificity and mechanism of chaperone action are lacking. α1-Antichymotrypsin (ACT) and α1-antitrypsin (α1-AT) are two closely related members of the serpin superfamily that aggregate through nucleation-dependent and nucleation-independent pathways, respectively. The sHsp α-crystallin was unable to prevent the nucleation-independent aggregation of α1-AT, whereas α-crystallin inhibited ACT aggregation in a dose-dependent manner. This selective inhibition of ACT aggregation coincided with the formation of a stable high molecular weight α-crystallin-ACT complex with a stoichiometry of 1 on a molar subunit basis. The kinetics of this interaction occur at the same rate as the loss of ACT monomer, suggesting that the monomeric species is bound by the chaperone. 4,4′-Dianilino-1,1′-binaphthyl-5,5′-disulfonic acid (Bis-ANS) binding and far-UV circular dichroism data suggest that α-crystallin interacts specifically with a non-native conformation of ACT. The finding that α-crystallin does not interact with α1-AT under these conditions suggests that α-crystallin displays a specificity for proteins that aggregate through a nucleation-dependent pathway, implying that the dynamic nature of both the chaperone and its substrate protein is a crucial factor in the chaperone action of α-crystallin and other sHsps.

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A Monash University Senior Logan Fellow and an NHMRC R. Douglas Wright Fellow.

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This work was supported in part by the Australian Research Council and the National Heath and Medical Research Council (NHMRC) via grants (to S. P. B. and J. A. C.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.