Effects of the protein environment on the structure and energetics of active sites of metalloenzymes. ONIOM study of methane monooxygenase and ribonucleotide reductase.

As the first application of our recently developed ONIOM2(QM:MM) and ONIOM3(QM:QM:MM) codes to the metalloenzymes with a large number of protein residues, two members of the non-heme protein family, methane monooxygenause and ribonucleotide reductase, have been chosen. The "active-site + four alpha-helical fragments" model was adopted which includes about 1000 atoms from 62 residues around the Fe-centered spheres. Comparison of the active-site geometries of MMOH and R2 units optimized with this model with those obtained with the "active site only" (with only 39-46 atoms) model and the X-ray results clearly demonstrates the crucial role of the active site-protein interaction in the enzymatic activities.