Involved in protein assisted folding. Part of the Cpn60 complex composed of 7 alpha and 7 beta subunits. Can also form a complex composed of 14 beta subunits only. Both complexes show ATPase activity. The Cpn60 complex interacts with the Cpn10 complex. Interacts with RAB during heat stress. Up-regulated by light. No visible phenotype; due to redundancy with CPN60B1. Cpn60B1 and cpn60B2 double mutant produces small albino seedlings. Assisted protein folding requires ATP hydrolysis, but not K(+) ions. Belongs to the chaperonin (HSP60) family.