Detailed active site configuration of a new crystal form of methanol dehydrogenase from Methylophilus W3A1 at 1.9 angstrom resolution

The three-dimensional structure of a new crystal form of methanol dehydroge nase from Methylophilus W3A1 has been obtained in the presence of substrate using data recorded at a synchrotron. The structure of this similar to 140 kDa heterotetramer, refined at 1.9 Angstrom resolution, reveals the detail ed configuration of its redox cofactor, pyrroloquinoline quinone (PQQ) C4, one of the oxygen-bearing atoms of this orthoquinone is in a planar configu ration while C5, which bears the other quinone oxygen, is tetrahedral, sugg esting that the PQQ is in the semiquinone redox state, The substrate bindin g site has been identified close to PQQ and to the side chain of Asp297, th e putative active site base. The proximity of the hydroxyl of methanol to C 5 of PQQ compared to the greater separation of the substrate methyl group f rom C5 supports the addition-elimination reaction mechanism involving a hem iketal intermediate.