GroEL from the psychrophilic bacterium Pseudoalteromonas haloplanktis TAC 125: molecular characterization and gene cloning

The heat shock response of the psychrophilic bacterium Pseudoalteromonas haloplanktis TAC 125 (PhTAC 125) gives rise to the production of several inducible proteins. Among these, the protein corresponding to a 55-kDa band on SDS-PAGE was purified to homogeneity and identified as a GroEL-like protein. The gene coding for this protein (PhGroEL) was cloned and sequenced; the deduced amino acid sequence shows 82% sequence identity to GroEL from Escherichia coli (EcGroEL). The ORF found in the 5' upstream region codes for a homologue of the GroES from E. coli (PhGroES, 71% sequence identity to EcGroES). PhGroEL shows a chaperone activity and can use GroES from E. coli as a co-chaperone. PhGroEL melting temperature, 6 degrees C lower than that of EcGroEL, and equilibrium unfolding experiments in urea showed a less stable protein architecture for the psychrophilic GroEL. The data herein reported demonstrate that PhGroEL cold adaptation consists in a shift of the protein properties toward lower temperatures without increasing catalytic efficiency at low temperatures. Primary extension analysis depicted a complex organization of regulative elements for the operon containing the genes coding for PhgroES and PhgroEL (PhgroE), suggesting that a fine-tuning of transcription can also be involved in thermal adaptation of PhTAC 125.