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 famil y of small heat-shock proteins (sHsps). According to the present model, bas ed on the in vitro experiments, sHsps are molecular chaperones that bind an d prevent aggregation of normative proteins during heat shock. Previously, we have shown that IbpA and IbpB bind to endogenous E. coli proteins aggreg ated intracellularly by heat shock, which can be separated from soluble pro teins 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 ser um. 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 am ounts 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 duri ng heat shock.