tailieunhanh - Báo cáo Y học: The role of zinc in the methylation of the coenzyme M thiol group in methanol:coenzyme M methyltransferase from Methanosarcina barkeri New insights from X-ray absorption spectroscopy

Methanol:coenzyme M methyltransferase from methanogenic archaea is a cobalamin-dependent enzyme composed of three different subunits: MtaA, MtaB and MtaC. MtaA is a zinc protein that catalyzes the methylation of coenzyme M (HS-CoM) with methylcob(III)alamin. We report zinc XAFS (X-ray absorption fine structure) results indicating that, in the absence of coenzyme M, zinc is probably coordinated by a single sulfur ligand and three oxygen or nitrogen ligands. In the presence of coenzyme M, one (N/O)-ligand was replaced by sulfur, most likely due to ligation of the thiol group of coenzyme M | Eur. J. Biochem. 269 2117-2123 2002 FEBS 2002 doi The role of zinc in the methylation of the coenzyme M thiol group in methanol coenzyme M methyltransferase from Methanosarcina barkeri New insights from X-ray absorption spectroscopy Markus Kriier1 Michael Haumann2 Wolfram Meyer-Klaucke3 Rudolf K. Thauer1 and Holger Dau2 1 Max-Planck-Institut fur terrestrische Mikrobiologie and Laboratorium fur Mikrobiologie Fachbereich Biologie der Philipps-Universitdt Marburg Germany 2Freie Universitbit Berlin Fachbereich Physik Berlin Germany 3DESY EMBL Outstation Hamburg Germany Methanol coenzyme M methyltransferase from methanogenic archaea is a cobalamin-dependent enzyme composed of three different subunits MtaA MtaB and MtaC. M laA is a zinc protein that catalyzes the methylation of coenzyme M HS-CoM with methylcob III alamin. We report inc XAFS X-ray absorption fine structure results indicating that in the absence of coenzyme M zinc is probably coordinated by a single sulfur ligand and three oxygen or nitrogen ligands. hl the presnnre of conn yrne M one N O -ligand was replaced by sulfur most likely due to ligation of the thiol group of coenzyme M. Multi ions in His237 or Cys239 which are proposed to be involved in ligating zinc resulted in an over 90 loss in enzyme activity and in distinct changes in the zinc the His237 fi Ala and Cys239 fi Ala mutants coenzyme M also seemed to bind efficiently by ligation to zinc indicating that some aspects of the zinc ligand environment are surprisingly uncritical for coenzyme M binding. Keywords zinc enzymes methanogenic archaea methyl transferases thiol group alkylation EXAFS. Methanosarcina barkeri and other Methanosarcina species can grow on methanol as carbon source which is dispro-portionated to CH4 and CO2 1 . Tlte first step m hlsis metabolic pathway is the formation of methyl-coenzyme M CH3-S-CoM from methanol and coenzyme M HS-CoM 2 . CH3OH HS-CoMMaA CH3-S-CoM H2O 1 AG kJ-mol-1