The crystal structure of methanol dehydrogenase (MDH) from Methylobacterium extorquens has been refined without stereochemical restraints at a resolution of 1.2 A. The high-resolution data have defined the conformation of the tricyclic pyrroloquinoline quinone (PQQ) cofactor ring as entirely planar. The detailed definition of the active-site geometry has shown many features that are similar to the quinohaemo-protein alcohol dehydrogenases from Comamonas testosteroni and Pseudomonas putida, both of which possess MDH-like and cytochrome c-like domains. Conserved features between the two types of PQQ-containing enzyme suggest a common pathway for electron transfer between MDH and its physiological electron acceptor cytochrome cL. A pathway for proton transfer from the active site to the bulk solvent is also suggested.