Two new oligomers of E. coli small heat‐shock protein IbpB identified under heat stress exhibit maximum holding chaperone activity

Abstract

Escherichia coli small heat‐shock protein IbpB (MW: 16 KDa) has holding chaperone activity and is present in cells at 30 °C as two large oligomers of MW 2.0–3.0 MDa and 600–700 KDa. We report here about the presence of two additional oligomers of MW around 400 and 130 KDa in cells under heat‐stress at 50 °C. These two smaller oligomers possess the most chaperone activity, as observed from the extent of inhibition of inactivation and aggregation separately, of L‐Lactate dehydrogenase in the presence of the individual oligomers at 52 and 60 °C, respectively. It is suggested here that the two larger oligomers act as poorly active storage forms, which under heat stress dissociate partially into smaller oligomers with high holdase activity.