Escherichia coli small heat shock protein IbpA is an aggregation-sensor that self-regulates its own expression at a translational level

Abstract

All organisms have protein quality control systems against stresses disturbing cellular protein homeostasis (proteostasis). The systems have multiple stages: folding, degradation, and sequestration. Sequestration of denatured proteins is the first step to support other maintenance strategies. Small heat shock proteins (sHsps), which are well-conserved chaperones, are representative “sequestrases” that co-aggregate with denatured proteins. We found that IbpA, an Escherichia coli sHsp, is a direct mediator for negative feedback regulation at the translational level. Recruitment of IbpA into the protein aggregates relieves the ibpA expression suppression. This novel mechanism of IbpA as an aggregation-sensor tightly regulates the IbpA level, enabling the sHsp to function as a sequestrase upon aggregation stress.