AN ANALYSIS OF THE ORIGINS OF A COOPERATIVE BINDING-ENERGY OF DIMERIZATION

The cooperativity between binding of cell wall precursor analogs (liga nds)to and antibiotic dimerization of the clinically important vancomy cin group antibiotics was investigated by nuclear magnetic resonance. When dimerization was weak in the absence of a ligand, the increase in the dimerization constant in the presence of a ligand derived largely from changes associated with tightening of the dimer interface. When dimerization was strong in the absence of a ligand,, the increase in t he dimerization constant in the presence of a ligand derived largely f rom changes associated with tightening of the ligand-antibiotic interf ace. These results illustrate how, when a protein has a loose structur e, the binding energy of another molecule to the protein can derive in part from changes occurring within the protein.