Local Flexibility of a New Single-Ring Chaperonin Encoded by Bacteriophage AR9 Bacillus subtilis .

Chaperonins, a family of molecular chaperones, assist protein folding in all domains of life. They are classified into two groups: bacterial variants and those present in endosymbiotic organelles of eukaryotes belong to group I, while group II includes chaperonins from the cytosol of archaea and eukaryotes. Recently, chaperonins of a prospective new group were discovered in giant bacteriophages; however, structures have been determined for only two of them. Here, using cryo-EM, we resolved a structure of a new chaperonin encoded by gene 228 of phage AR9 B. subtilis . This structure has similarities and differences with members of both groups, as well as with other known phage chaperonins, which further proves their diversity.