A QUANTITATIVE ASSESSMENT OF THE ROLE OF CHAPERONIN PROTEINS IN PROTEIN-FOLDING IN-VIVO

In vitro the chaperonin proteins, GroEL and GroES, facilitate the fold ing of some other proteins under conditions where that process does no t occur spontaneously, Using values drawn from a number of such in vit ro 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 eases are examined, wher e compelling evidence points to the involvement of the chaperonins; th e in vivo folding of the bacteriophage coat protein during the burst p hase of phage morphogenesis and of Rubisco during chloroplast developm ent and during expression of recombinant Rubisco in E. coli. In each c ase the maximum in vitro rates are nearly sufficient to account for th e observed in vivo rates of formation of the native protein, However, in general, there appears to be sufficient GroEL and GroES to facilita te the folding of no more than 5% of all of the proteins within E. col i.