ibpA

IbpA, or inclusion body protein A, is a bacterial small heat shock protein (sHSP) that functions as a molecular chaperone to protect proteins from aggregation during stress. In Escherichia coli and many other bacteria, IbpA is encoded by the ibpA gene and is usually co-expressed with ibpB in an adjacent operon. The IbpA and IbpB proteins can form large oligomeric complexes and often act together to stabilize vulnerable substrate proteins in the cytosol during heat or other stresses.

Mechanism: IbpA binds to partially unfolded or denatured proteins in an ATP-independent manner, preventing irreversible aggregation and preserving substrates for refolding by ATP-dependent chaperone systems such as DnaK/DnaJ/GrpE (Hsp70) and the disaggregase ClpB. During recovery, substrate proteins can be released for refolding.

Structure: IbpA belongs to the alpha-crystallin domain family of small heat shock proteins. It has a conserved α-crystallin domain flanked by flexible N- and C-terminal extensions that promote dynamic oligomerization. In cells, IbpA/B form dynamic oligomers that can remodel in response to cellular conditions.

Regulation and role: IbpA expression is upregulated by the heat shock response, primarily under control of the sigma factor RpoH (σ32). It is induced by elevated temperatures and other stresses and contributes to cellular thermotolerance and protein quality control, though it is not essential for viability in many bacteria.

Distribution: The IbpA/B system is conserved across diverse bacteria and is often studied as part of the bacterial heat shock regulon.