Ghosh M, Anthony C, Harlos K, Goodwin M G, Blake C
Laboratory of Molecular Biophysics, University of Oxford, UK.
Structure. 1995 Feb 15;3(2):177-87. doi: 10.1016/s0969-2126(01)00148-4.
Methanol dehydrogenase (MDH) is a bacterial periplasmic quinoprotein; it has pyrrolo-quinoline quinone (PQQ) as its prosthetic group, requires Ca2+ for activity and uses cytochrome cL as its electron acceptor. Low-resolution structures of MDH have already been determined.
The structure of the alpha 2 beta 2 tetramer of MDH from Methylobacterium extorquens has now been determined at 1.94 A with an R-factor of 19.85%.
The alpha-subunit of MDH has an eight-fold radial symmetry, with its eight beta-sheets stabilized by a novel tryptophan docking motif. The PQQ in the active site is held in place by a coplanar tryptophan and by a novel disulphide ring formed between adjacent cysteines which are bonded by an unusual non-planar trans peptide bond. One of the carbonyl oxygens of PQQ is bonded to the Ca2+, probably facilitating attack on the substrate, and the other carbonyl oxygen is out of the plane of the ring, confirming the presence of the predicted free-radical semiquinone form of the prosthetic group.
甲醇脱氢酶（MDH）是一种细菌周质醌蛋白；它以吡咯喹啉醌（PQQ）作为辅基，活性需要Ca2+，并以细胞色素cL作为电子受体。MDH的低分辨率结构已经确定。
现在已确定来自嗜甲基菌的MDH的α2β2四聚体结构，分辨率为1.94 Å，R因子为19.85%。
MDH的α亚基具有八重径向对称性，其八个β折叠通过一种新型色氨酸对接基序得以稳定。活性位点中的PQQ通过一个共平面色氨酸以及相邻半胱氨酸之间形成的一个新型二硫环固定在位，这些半胱氨酸通过一个不寻常的非平面反式肽键相连。PQQ的一个羰基氧与Ca2+结合，可能有助于对底物的攻击，另一个羰基氧不在环平面内，证实了辅基预测的自由基半醌形式的存在。
