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An Open-Faced Chaperonin: Crystal Structures of a Group II Chaperonin Reveal Open and Cosed States Print
Thursday, 16 September 2010 14:37

Chaperonins are complexes that promote the proper folding of newly synthesized or denatured proteins by encapsulating them in a protective shell. Chaperonins come in two classes, group I and group II, which differ in their localization and closing requirements; group I members require a ring-shaped cofactor to fully close the folding chamber whereas group II members contain a built-in “lid.” Interestingly, as of yet, the structures of group II chaperonins have only been solved in the closed conformation, but in this Paper of the Week, Jose Pereira and colleagues present crystal structures of the group II chaperonin from the archaeal Methanococcus maripaludis in both closed and open states. This comparative information revealed that the closing mechanism for group II chaperonins is quite distinct from group I; during closing, all three domains—equatorial, apical, and intermediate—rotate as a single rigid body, whereas in group I chaperonins the equatorial domains remain relatively stationary. As a result, there is a significant reduction in the size and shape of the folding chamber during closing. However, substrate binding sites and sites for allosteric regulation are conserved between the two groups, suggesting they arose from a common ancestor. Together, the structures shed new light on this important class of proteins. Article Link (PDF)