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The IbpA and IbpB small heat‐shock proteins are substrates of the AAA+ Lon protease
Author(s) -
Bissonnette Sarah A.,
RiveraRivera Izarys,
Sauer Robert T.,
Baker Tania A.
Publication year - 2010
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2010.07070.x
Subject(s) - biology , escherichia coli , protease , heat shock protein , conserved sequence , enzyme , biochemistry , biophysics , peptide sequence , microbiology and biotechnology , gene
Summary Small heat‐shock proteins (sHSPs) are a widely conserved family of molecular chaperones, all containing a conserved α‐crystallin domain flanked by variable N‐ and C‐terminal tails. We report that IbpA and IbpB, the sHSPs of Escherichia coli , are substrates for the AAA+ Lon protease. This ATP‐fueled enzyme degraded purified IbpA substantially more slowly than purified IbpB, and we demonstrate that this disparity is a consequence of differences in maximal Lon degradation rates and not in substrate affinity. Interestingly, however, IbpB stimulated Lon degradation of IbpA both in vitro and in vivo . Furthermore, although the variable N‐ and C‐terminal tails of the Ibps were dispensable for proteolytic recognition, these tails contain critical determinants that control the maximal rate of Lon degradation. Finally, we show that E. coli Lon degrades variants of human α‐crystallin, indicating that Lon recognizes conserved determinants in the folded α‐crystallin domain itself. These results suggest a novel mode for Lon substrate recognition and provide a highly suggestive link between the degradation and sHSP branches of the protein quality‐control network.