Chaperonins: In life and death

The Hsp60 family proteins, also known as “chaperonins”, are a highly conserved subgroup of molecular chaperones found in all organisms with many species having multiple forms. This family includes the bacterial GroEL, mitochondrial Hsp60, plastid Rubisco subunit binding protein, archaeagroup II chaperonins and eukaryotic cytosolic TCP-1 proteins. These proteins are usually expressed constitutively but some of these are also stress inducible. Apart from being essential for correct folding of the nascent polypeptides, Hsp60 proteins have critical roles in sorting/refolding and stabilizing proteins denatured during stress. Likewise, the cytosolic Hsp60/TCP-1 complex is vital for the folding Correspondence/Reprint request: Dr. Subhash C. Lakhotia, Cytogenetics Laboratory, Department of Zoology Banaras Hindu University, Varanasi 221 005, India. E-mail: [email protected] Surajit Sarkar et al. 44 and assembly of tubulin and actin cytoskeletal components. Besides the chaperoning activities, Hsp60 family proteins have important roles in immunity, cell signaling, apoptosis and fertility. Multiple forms of Hsp60 family proteins in different species have acquired novel functions that appear to be independent of their basic chaperoning activities. Hsp60, thus, is a typical example of “moonlighting proteins” essential for life as well as death of the cell.