Implicated in mitochondrial protein import and macromolecular assembly. May facilitate the correct folding of imported proteins. May also prevent misfolding and promote the refolding and proper assembly of unfolded polypeptides generated under stress conditions in the mitochondrial matrix. By heat shock. There are multiple isoforms that, with increasing temperature, shift in relative abundance from the more basic to the more acidic. Exists in at least five isoforms that are not related by a simple post-translational modification and may represent the products of different genes. Belongs to the chaperonin (HSP60) family.