Multielectron redox catalysis is at the heart of bioenergetics. In many enzymes catalyzing multielectron reactions, the active site is linked to the exchange of single electrons with the redox partner via a chain of [FeS] clusters (Fig. 1). Although it is usually presumed that electron transfer through these clusters is fast so that it has little impact on catalysis, there is mounting evidence that this is often not the case, and intramolecular electron transfer can play crucial roles in modulating catalytic activity.1 Our long term goal is to understand how ensembles of redox cofactors are tuned to control multielectron chemistry and exploit this knowledge to construct catalysts for energy applications. Hydrogenases catalyze the interconversion of hydrogen to protons and electrons. This is a keyreaction in the energy economies of microbes and humans, and there is interest in understanding the mechanisms both to develop technologies and as models for multielectron catalysis. Two key questions have arisen. First, how is oxygen tolerance achieved in some [NiFe]-hydrogenases? Second, how is the catalytic bias tuned? Our hypothesis is that electronic interactions between accessory [FeS] clusters and the [NiFe] site play a large role in tuning these properties. This hypothesis is based on the following observations. First, oxygen tolerant uptake [NiFe]-hydrogenases have conserved changes near the proximal [FeS] cluster, and this cluster may have unusual coordination and electronic properties (Fig. 2).2 Second, our preliminary results demonstrate that the bidirectional multimeric [NiFe]-hydrogenases do not have an overwhelming bias toward hydrogen oxidation.3 Furthermore, the bidirectional hydrogenases do not contain a conserved [3Fe4S] cluster found in all uptake enzymes, and the EPR signatures of these enzymes suggest unexpected couplings between centers. Based on these observations, the focus of this proposal is to alter the catalytic bias and susceptibility to aerobic inactivation of multimeric, bidirectional [NiFe]-hydrogenases by mutating residues surrounding the proximal [FeS] cluster. Characterization of the properties of these mutants will provide a comprehensive understanding of the roles played by the [FeS] clusters in controlling catalysis.
|Effective start/end date||7/1/12 → 6/30/18|
- US Department of Energy (DOE): $750,000.00
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