IbpA/B small heat-shock protein of marine bacterium Vibrio harveyi binds to proteins aggregated in a cell during heat shock.

The IbpA and IbpB are 16-kDa Escherichia coli proteins belonging to a family of small heat-shock proteins (sHsps). According to the present model, based on the in vitro experiments, sHsps are molecular chaperones that bind and prevent aggregation of nonnative proteins during heat shock. Previously, we have shown that IbpA and IbpB bind to endogenous E. coli proteins aggregated intracellularly by heat shock, which can be separated from soluble proteins and membranes in sucrose density gradients (fraction S). In this work we have found that marine bacterium Vibrio harveyi contains a single sHsp which is strongly induced by heat shock and reacts with the anti-IbpA/B serum. The 26 amino-terminal amino acids of this sHsp bear high homology to E. coli IbpA and IbpB proteins (73% and 54% identity, respectively). Fraction S was prepared from heat-shocked cells of V. harveyi, it contained high amounts of the IbpA/B protein. This result indicates that the IbpA/B protein of V. harveyi binds to the proteins that aggregate in V. harveyi cells during heat shock.