THE ALLOSTERIC MECHANISM OF THE CHAPERONIN GROEL - A DYNAMIC ANALYSIS

Normal mode calculations on individual subunits and a multisubunit con struct are used to analyze the structural transitions that occur durin g the GroEL cycle. The normal modes demonstrate that the specific disp lacements of the domains (hinge bending, twisting) observed in the str uctural studies arise from the intrinsic flexibility of the subunits. The allosteric mechanism (positive cooperativity within a ring, negati ve cooperativity between rings) is shown to be based on coupled tertia ry structural changes, rather than the quaternary transition found in classic allosteric proteins. The results unify static structural data from x-ray crystallography and cryoelectron microscopy with functional measurements of binding and cooperativity.