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Project Progress

We have been using a variety of different approaches to examine the evolutionary trajectories and evolutionary origins of nitrogen fixation, hydrogen metabolism, and photosynthesis. These are all three complicated biochemical processes that instead of being mediated by simply one or two gene product(s) require large suites of genes. For these three processes the main biochemical machinery; nitrogenase for nitrogen fixation, hydrogenase for hydrogen metabolisms, photosystems for photsynthesis, require specific gene products for the synthesis and assembly of complex prosthetic groups that are integral and essential for their respective functions. The requirement for numerous gene products for these enzymes allows use to probe the phylogenetic trajectories of suite of genes to trace evolutionary relatedness and trajectories and is a much more robust approach than simply basing inheritance on a single gene. In addition, the processes of nitrogen and photosynthesis are intimately linked since the nitrogenase structural genes and key enzymes in dark chlorophyll biosynthesis are related by gene duplication. For hydrogen metabolism [FeFe]-hydrogenases and [NiFe]-hydrogenases are related to our strongly related to other enzymes. The [FeFe]-hydrogenase are related to a protein called Nar1p that is only found in eukaryotes and implicated in being involved in iron-sulfur cluster biosynthesis in the cytosol. The [NiFe]-hydrogenases are related to respiratory complex I suggesting that H₂ itself may have been a predecessor to NADH in early metabolism. Probing evolutionary trajectories of the processes that are central to the ABRCs thrust is rapidly developing has been thus far quite fruitful. Using this approach we have been able to implicate that the complex biosynthetic machinery involved in the synthesis of the active site complex iron-sulfur clusters and maturation of active Mo-nitrogenase and [FeFe]-hydrogenase was adapted after the structural genes were apparently recruited for the process. Further the results indicate, as perhaps anticipated in retrospect, that these enzymes as we see them today with their complicated cofactors are not likely to be that old. We have also to infer in preliminary work that the active sites of [NiFe]-hydrogenases and carbon monoxide dehydrogenases probably follow a distinctly different evolutionary path and are likely to be more ancient. For Mo-nitrogenase we are able to infer that the most ancient of extant forms of this active enzyme occur in the methanogenic Archaea. The results have paved the way for challenging paradigms regarding the evolutionary path of complex iron-sulfur enzymes and have allowed us to rationalize a clear hypothetical path that we can examine through further experimentation and analysis.