Biochemistry, Department of
Date of this Version
2004
Citation
The Journal of Biological Chemistry, Vol. 279, No. 9, Issue of February 27, pp. 7566–7575, 2004
Abstract
The small heat shock proteins (sHSPs) are a ubiquitous
class of ATP-independent chaperones believed to
prevent irreversible protein aggregation and to facilitate
subsequent protein renaturation in cooperation
with ATP-dependent chaperones. Although sHSP chaperone
activity has been studied extensively in vitro, understanding
the mechanism of sHSP function requires
identification of proteins that are sHSP substrates in
vivo. We have used both immunoprecipitation and affinity
chromatography to recover 42 proteins that specifically
interact with Synechocystis Hsp16.6 in vivo during
heat treatment. These proteins can all be released from
Hsp16.6 by the ATP-dependent activity of DnaK and cochaperones
and are heat-labile. Thirteen of the putative
substrate proteins were identified by mass spectrometry
and reveal the potential for sHSPs to protect cellular
functions as diverse as transcription, translation, cell
signaling, and secondary metabolism. One of the putative
substrates, serine esterase, was purified and tested
directly for interaction with purified Hsp16.6. Hsp16.6
effectively formed soluble complexes with serine esterase
in a heat-dependent fashion, thereby preventing formation
of insoluble serine esterase aggregates. These
data offer critical insights into the characteristics of
native sHSP substrates and extend and provide in vivo
support for the chaperone model of sHSP function.
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Comments
Copyright 2004 by The American Society for Biochemistry and Molecular Biology, Inc.