Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, 321 Church Street SE, Minneapolis, Minnesota 55455, United States.
Biochemistry. 2011 Apr 12;50(14):2931-8. doi: 10.1021/bi200023n. Epub 2011 Mar 16.
MauG is a diheme enzyme responsible for the post-translational formation of the catalytic tryptophan tryptophylquinone (TTQ) cofactor in methylamine dehydrogenase (MADH). MauG can utilize hydrogen peroxide, or molecular oxygen and reducing equivalents, to complete this reaction via a catalytic bis-Fe(IV) intermediate. Crystal structures of diferrous, Fe(II)-CO, and Fe(II)-NO forms of MauG in complex with its preMADH substrate have been determined and compared to one another as well as to the structure of the resting diferric MauG-preMADH complex. CO and NO each bind exclusively to the 5-coordinate high-spin heme with no change in ligation of the 6-coordinate low-spin heme. These structures reveal likely roles for amino acid residues in the distal pocket of the high-spin heme in oxygen binding and activation. Glu113 is implicated in the protonation of heme-bound diatomic oxygen intermediates in promoting cleavage of the O-O bond. Pro107 is shown to change conformation on the binding of each ligand and may play a steric role in oxygen activation by positioning the distal oxygen near Glu113. Gln103 is in a position to provide a hydrogen bond to the Fe(IV)═O moiety that may account for the unusual stability of this species in MauG.
MauG 是一种二血红素酶，负责在单胺脱氢酶 (MADH) 中催化色氨酸色氨酰醌 (TTQ) 辅因子的翻译后形成。MauG 可以利用过氧化氢或分子氧和还原当量，通过催化双 Fe(IV) 中间产物完成此反应。已经确定了 MauG 与前 MADH 底物复合物中二价铁、Fe(II)-CO 和 Fe(II)-NO 形式的晶体结构，并将其彼此以及与静止的二价铁 MauG-前 MADH 复合物的结构进行了比较。CO 和 NO 各自都仅与 5 配位高自旋血红素结合，而 6 配位低自旋血红素的配位没有变化。这些结构揭示了氨基酸残基在高自旋血红素的远端口袋中在氧结合和活化中的可能作用。Glu113 可能参与了质子化血红素结合的双原子氧中间体，以促进 O-O 键的断裂。脯氨酸 107 被证明在结合每种配体时都会改变构象，并且可能通过将远端氧定位在 Glu113 附近在氧活化中发挥空间位阻作用。Gln103 处于可以与 Fe(IV)═O 部分形成氢键的位置，这可能解释了 MauG 中该物种的异常稳定性。
