ATP-enhanced molecular chaperone functions of the small heat shock protein human αB crystallin

ATP-enhanced molecular chaperone functions of the small heat shock protein human αB crystallin

Paul J. Muchowski* and
John I. Clark*,†,‡

Departments of ^*Biological Structure, Box 357420, and ^†Ophthalmology, Box 356485, University of Washington, Seattle, WA, 98195-7420

Communicated by George B. Benedek, Massachusetts Institute of Technology, Cambridge, MA (received for review June 16, 1997)

Abstract

We report direct experimental evidence that human αB-crystallin, a member of the small heat shock protein family, actively participates in the refolding of citrate synthase (CS) in vitro. In the presence of 3.5 mM ATP, CS reactivation by αB-crystallin was enhanced approximately twofold. Similarly, 3.5 mM ATP enhanced the chaperone activity of αB-crystallin on the unfolding and aggregation of CS at 45°C. Consistent with these findings, cell viability at 50°C was improved nearly five orders of magnitude in Escherichia coli expressing αB-crystallin. SDS/PAGE analysis of cell lysates suggested that αB-crystallin protects cells against physiological stress in vivo by maintaining cytosolic proteins in their native and functional conformations. This report confirms the action of αB-crystallin as a molecular chaperone both in vitro and in vivo and describes the enhancement of αB-crystallin chaperone functions by ATP.

Footnotes

↵ ‡ To whom reprint requests should be addressed. e-mail: clarkji{at}u.washington.edu.
ABBREVIATIONS:

Hsp,

heat shock protein;

sHsp,

small Hsp;

CS,

citrate synthase;

CFUs,

colony forming units