A quantitative assessment of the role of the chaperonin proteins in protein folding in vivo.

In vitro the chaperonin proteins, GroEL and GroES, facilitate the folding of some other proteins under conditions where that process does not occur spontaneously. Using values drawn from a number of such in vitro studies, together with the known rates of in vivo protein synthesis by Escherichia coli and the known quantities of GroEL and GroES in E. coli, an assessment of the general role of these proteins in protein folding in vivo has been made. Three specific cases are examined, where compelling evidence points to the involvement of the chaperonins; the in vivo folding of the bacteriophage coat protein during the burst phase of phage morphogenesis and of Rubisco during chloroplast development and during expression of recombinant Rubisco in E. coli. In each case the maximum in vitro rates are nearly sufficient to account for the observed in vivo rates of formation of the native protein. However, in general, there appears to be sufficient GroEL and GroES to facilitate the folding of no more than 5% of all of the proteins within E. coli.