RESIDUE LYSINE-34, IN GROES MODULATES ALLOSTERIC TRANSITIONS IN GROEL

The conserved residue Lys-34 in GroES was replaced by alanine and glut amic acid using site-directed mutagenesis. This residue is near the ca rboxy terminus of the mobile loop in GroES (residues 17-32) which beco mes immobilized upon formation of the GroEL/GroES complex [Landry et a l. (1993) Nature 364, 255-258]. Both charge neutralization (Lys-34-->A la) and charge reversal (Lys-34--->Glu) at this position have little e ffect on the binding constant of GroES to GroEL, but they increase the enhancement by GroES of cooperativity in ATP hydrolysis by GroEL. Thi s is reflected by a change in the Hill coefficient (at 10 mM K+) from 4.10 (+/-0.22) in the presence of wild-type GroES to 5.17 (+/-0.24) an d 4.46 (+/-0.14) in the presence of the GroES mutants Lys-34-->Ala and Lys-34-->Glu, respectively. The results are interpreted using the Mon od-Wyman-Changeux (MWC) model for cooperativity [Monod et al. (1965) J . Mol. Biol. 12, 88-118]. They suggest that Lys-34 in GroES modulates the allosteric transition in GroEL by stabilizing a relaxed (R)-like s tate.