   1.1.2.8 | to 2.6 A resolution, by molecular replacement. Eight W-shaped beta-sheet motifs are arranged circularly in a propeller-like fashion forming a disk-shaped superbarrel. The prosthetic group is located in the centre of the superbarrel and is coordinated to a calcium ion. Most amino acid residues found in close contact with the prosthetic group pyrroloquinoline quinone and the Ca2+ are conserved between the quinoprotein ethanol dehydrogenase structure and that of the methanol dehydrogenases from Methylobacterium extorquens or Methylophilus W3A1. The main differences in the active-site region are a bulky tryptophan residue in the active-site cavity of methanol dehydrogenase, which is replaced by a phenylalanine and a leucine side-chain in the ethanol dehydrogenase structure and a leucine residue right above the pyrrolquinoline quinone group in methanol dehydrogenase which is replaced by a tryptophan side-chain. Both amino acid exchanges contribute to different substrate specificities of these otherwise very similar enzymes. In addition to the Ca2+ in the active-site cavity, ethanol dehydrogenase contains a second Ca2+-binding site at the N-terminus, which contributes to the stability of the native enzyme |
