Structural and functional diversity of novel and known bacteriophage-encoded chaperonins

A bioinformatics analysis of the currently predicted GroEL-like proteins encoded by bacteriophage genomes was carried out in comparison with the phage double-ring EL and single-ring OBP chaperonins, previously described by us, as well as with the known chaperonins of group I and group II. A novel GroEL-like protein predicted in the genome of phage AR9 Bacillus subtilis was expressed in E. coli cells, purified and characterised by various physicochemical methods. As shown by native electrophoresis, analytical ultracentrifugation and single-particle electron microscopy analysis, the putative AR9 chaperonin is a single-ring heptamer. Like the EL and OBP chaperonins, the new AR9 chaperonin possesses chaperone activity and does not require co-chaperonin to function. It was shown to prevent aggregation and provide refolding of the denatured substrate protein, endolysin, in an ATP-dependent manner. A comparison of its structural and biochemical properties with those of the EL and OBP chaperonins suggests outstanding diversity in this group of phage chaperonins.