CRYSTAL-STRUCTURE OF DIMETHYL-SULFOXIDE REDUCTASE FROM RHODOBACTER-CAPSULATUS AT 1.88 ANGSTROM RESOLUTION

The periplasmic dimethyl sulfoxide reductase (DMSOR) from the photosyn thetic purple bacterium Rhodobacter capsulatus functions as the termin al electron acceptor in its respiratory chain. The enzyme catalyzes th e reduction of highly oxidized substrates like dimethyl sulfoxide to d imethyl sulfide. At a molybdenum redox center, two single electrons ar e transferred from cytochrome c(556) to the substrate dimethyl sulfoxi de, generating dimethyl sulfide and (with two protons) water. The enzy me was purified and crystallized in space group P4(1)2(1)2 with unit c ell dimensions of a = b = 80.7 Angstrom and c = 229.2 Angstrom. The cr ystals diffract beyond 1.8 Angstrom with synchrotron radiation. The th ree-dimensional structure was solved by a combination of multiple isom orphous replacement and molecular replacement techniques. The atomic m odel was refined to an R-factor of 0.169 for 57,394 independent reflec tions. The spherical protein consists of four domains with a funnel-li ke cavity that leads to the freely accessible metal-ion redox center. The bis(molybdopterin guanine dinucleotide)molybdenum cofactor (1541 D a) of the single chain protein (85,033 Da) has the molybdenum ion boun d to the cis-dithiolene group of only one molybdopterin guanine dinucl eotide molecule. Three additional ligands, two oxo groups and the oxyg en of a serine side-chain, are bound to the molybdenum ion. The second molybdopterin system is not part of the ligand sphere of the metal ce nter with its sulfur atoms at distances of 3.5 Angstrom and 3.8 Angstr om away. It might be involved in electron shuttling from the protein s urface to the molybdenum center. (C) 1996 Academic Press Limited