Chaperones কী?

A molecular chaperone is a protein that assists the folding of others without becoming part of them or supplying information about the fold: it prevents the aggregation that competes with folding in the crowded cytoplasm. Hsp70 binds exposed hydrophobic segments of nascent or unfolded chains, releasing them on ATP hydrolysis for another attempt; the chaperonin GroEL (Hsp60 in mitochondria, TRiC in the eukaryotic cytosol) is a double barrel of fourteen subunits whose central cavity, capped by GroES, encloses a single chain of up to $60\,\mathrm{kDa}$ in isolation for about ten seconds — an Anfinsen cage — and ejects it whether folded or not, to try again. About a tenth of newly made bacterial proteins pass through GroEL, and a cell whose chaperones are overwhelmed — by heat, which is why most are heat-shock proteins induced by a rise in temperature — fills with aggregates.