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Pyranopterin Coordination Controls Molybdenum Electrochemistry in Escherichia coli Nitrate Reductase.


ABSTRACT: We test the hypothesis that pyranopterin (PPT) coordination plays a critical role in defining molybdenum active site redox chemistry and reactivity in the mononuclear molybdoenzymes. The molybdenum atom of Escherichia coli nitrate reductase A (NarGHI) is coordinated by two PPT-dithiolene chelates that are defined as proximal and distal based on their proximity to a [4Fe-4S] cluster known as FS0. We examined variants of two sets of residues involved in PPT coordination: (i) those interacting directly or indirectly with the pyran oxygen of the bicyclic distal PPT (NarG-Ser(719), NarG-His(1163), and NarG-His(1184)); and (ii) those involved in bridging the two PPTs and stabilizing the oxidation state of the proximal PPT (NarG-His(1092) and NarG-His(1098)). A S719A variant has essentially no effect on the overall Mo(VI/IV) reduction potential, whereas the H1163A and H1184A variants elicit large effects (?Em values of -88 and -36 mV, respectively). Ala variants of His(1092) and His(1098) also elicit large ?Em values of -143 and -101 mV, respectively. An Arg variant of His(1092) elicits a small ?Em of +18 mV on the Mo(VI/IV) reduction potential. There is a linear correlation between the molybdenum Em value and both enzyme activity and the ability to support anaerobic respiratory growth on nitrate. These data support a non-innocent role for the PPT moieties in controlling active site metal redox chemistry and catalysis.

SUBMITTER: Wu SY 

PROVIDER: S-EPMC4599019 | biostudies-literature | 2015 Oct

REPOSITORIES: biostudies-literature

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Pyranopterin Coordination Controls Molybdenum Electrochemistry in Escherichia coli Nitrate Reductase.

Wu Sheng-Yi SY   Rothery Richard A RA   Weiner Joel H JH  

The Journal of biological chemistry 20150821 41


We test the hypothesis that pyranopterin (PPT) coordination plays a critical role in defining molybdenum active site redox chemistry and reactivity in the mononuclear molybdoenzymes. The molybdenum atom of Escherichia coli nitrate reductase A (NarGHI) is coordinated by two PPT-dithiolene chelates that are defined as proximal and distal based on their proximity to a [4Fe-4S] cluster known as FS0. We examined variants of two sets of residues involved in PPT coordination: (i) those interacting dire  ...[more]

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