Dissecting intrinsic chaperonin activity

It has long been known that the linear sequence of amino acids along the polypeptide chains contains all the necessary information required to determine the correct three-dimensional structure of a protein (1). Indeed, a large number of proteins have been shown to refold spontaneously in vitro from an unfolded denatured state to the native folded state (2–6). Other proteins, often large ones, however, do not refold spontaneously in high yields. This is usually due to irreversible aggregation of unfolded or partially folded states (7–9). Such proteins require the presence of ancillary proteins known as chaperonins to assist in the folding process (10–13). The two best studied chaperonins are the Escherichia coli GroEL and GroES chaperonins which act in concert (for reviews, see refs. 14–18). GroEL has a cage-like double ring structure with two internal cavities, each ring comprising seven identical (≈15 kDa) subunits; GroES caps one end of the GroEL double ring and consists of a single ring of seven (≈10 kDa) identical subunits (19–21). In vivo intact GroEL, GroES, and ATP are required for function (14–18, 22, 23). There are several features of the chaperonins that have been considered a key to their activity: ( i ) the ability to unfold incorrectly folded, kinetically trapped intermediates, …