chaperonin families, type I and type II. Chaperonins are involved in productive folding of proteins. They share a common general morphology, a double toroid of 2 stacked rings, each composed of 7-9 subunits. There are 2 main chaperonin groups. The symmetry of type I is seven-fold and they are found in eubacteria (GroEL) and in organelles of eubacterial descent (hsp60 and RBP). The symmetry of type II is eight- or nine-fold and they are found in archea (thermosome), thermophilic bacteria (TF55) and in the eukaryotic cytosol (CTT). Their common function is to sequester nonnative proteins inside their central cavity and promote folding by using energy derived from ATP hydrolysis.
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