title: A variant conferring cofactor-dependent assembly of Escherichia coli dimethylsulfoxide reductase.
abstract: We have investigated the final steps of complex iron-sulfur molybdoenzyme (CISM) maturation using Escherichia coli DMSO reductase (DmsABC) as a model system. The catalytic subunit of this enzyme, DmsA, contains an iron-sulfur cluster (FS0) and a molybdo-bis(pyranopterin guanine dinucleotide) cofactor (Mo-bisPGD). We have identified a variant of DmsA (Cys59Ser) that renders enzyme maturation sensitive to molybdenum cofactor availability. DmsA-Cys59 is a ligand to the FS0 [4Fe-4S] cluster. In the presence of trace amounts of molybdate, the Cys59Ser variant assembles normally to the cytoplasmic membrane and supports respiratory growth on DMSO, although the ground state of FS0 as determined by EPR is converted from high-spin (S=3/2) to low-spin (S=1/2). In the presence of the molybdenum antagonist tungstate, wild-type DmsABC lacks Mo-bisPGD, but is translocated via the Tat translocon and assembles on the periplasmic side of the membrane as an apoenzyme. The Cys59Ser variant cannot overcome the dual insults of amino acid substitution plus lack of Mo-bisPGD, leading to degradation of the DmsABC subunits. This indicates that the cofactor can serve as a chemical chaperone to mitigate the destabilizing effects of alteration of the FS0 cluster. These results provide insights into the role of the Mo-bisPGD-protein interaction in stabilizing the tertiary structure of DmsA during enzyme maturation.
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Huipo
authors.initials: H
authors.lastname: Tang
authors.forename: Richard A
authors.initials: RA
authors.lastname: Rothery
authors.forename: Joel H
authors.initials: JH
authors.lastname: Weiner
mesh_terms: D003067:Coenzymes / Q000502:physiology*; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000201:enzymology*; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008667:Metalloproteins / Q000502:physiology*; D000090006:Molybdenum Cofactors; D010088:Oxidoreductases / Q000737:chemistry*; D011621:Pteridines; D017973:Tungsten Compounds / Q000494:pharmacology
chemical_list: D003067:Coenzymes; D004121:Dimethyl Sulfoxide; D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D000090006:Molybdenum Cofactors; D010088:Oxidoreductases; D011621:Pteridines; D017973:Tungsten Compounds; C022261:molybdopterin; C045664:dimethyl sulfoxide reductase; C045951:tungstate