Molecular mechanism for dimerization to regulate the catalytic activity ofhuman cytomegalovirus protease

Biochemical studies indicate that dimerization is required for the catalyti c activity of herpesvirus proteases, whereas structural studies show a comp lete active site in each monomer, away from the dimer interface. Here we re port kinetic, biophysical and crystallographic characterizations of structu re-based mutants in the dimer interface of human cytomegalovirus (HCMV) pro tease. Such mutations can produce a 1,700-fold reduction in the k(cat) whil e having minimal effects on the K-m. Dinner stability is not affected by th ese mutations, suggesting that dimerization itself is insufficient for acti vity. There are large changes in monomer conformation and dimer organizatio n of the apo S225Y mutant enzyme. However, binding of an activated peptidom imetic inhibitor induced a conformation remarkably similar to the wild type protease. our studies suggest that appropriate dimer formation may be requ ired to indirectly stabilize the protease oxyanion hole, revealing a novel mechanism for dimerization to regulate enzyme activity.