The roles of the Escherichia coli lbpA and lbpB chaperones in protection of heat-denatured proteins against irreversible aggregation in vivo were investigated. Overproduction of lbpA and lbpB resulted in stabilization of the denatured and reversibly aggregated proteins (the S fraction), which could be isolated from E. coli cells by sucrose gradient centrifugation. This finding is in agreement with the present model of the small heat-shock proteins' function, based mainly on in vitro studies. Deletion of the ibpAB operon resulted in almost twofold increase in protein aggregation and in inactivation of an enzyme (fructose-1,6-biphosphate aldolase) in cells incubated at 50 degreesC for 4 h, decreased efficiency of the removal of protein aggregates formed during prolonged incubation at 50 degreesC and affected cell viability at this temperature. IbpA/B proteins were not needed for removal of protein aggregates or for the enzyme protection/renaturation in cells heat shocked at 50 degreesC for 15 min. These results show that the IbpA/B proteins are required upon an extreme, long-term heat shock. Overproduction of lbpA but not lbpB caused an increase of the level of beta-lactamase precursor, which was localized in the S fraction, together with the lbpA protein, which suggests that the unfolded precursor binds to lbpA but not to lbpB. Although in the wild-type cells both E. coli small heat-shock proteins are known to localize in the S fraction, only 2% of total lbpB co-localized with the aggregated proteins in the absence of lbpA, while in the absence of lbpB, the majority of lbpA was present in the aggregates fraction.
|Number of pages||9|
|Publication status||Published - 1 Jun 2002|
- protein aggregation
- beta-lactamase precursor