Title: Investigating possible evolutionary routes to molybdoenzymes

Speaker: Dr. Yamei Li (Center for Sustainable Resource Science, RIKEN)

Abstract:

All life forms depend on redox reactions for energy transduction and conservation to accomplish metabolism, reproduction, etc. The emergence of life likely occurred with an increase in complexity of both cellular structure and metabolism, which ultimately relied on an enhanced energy transduction efficiency/rate through catalysis. One plausible scenario for a predictive evolution is that transition metal containing minerals function as enzymatic analogues for catalyzing chemical conversions; and the minerals will finally transform/evolve into proto-enzymes with higher efficiency and specificity. Understanding mineral surface catalysis in relationship to energy flow and anabolism which may have contributed to the emergence of life is thus important. In nature, the molybdenum-pterin active center features a highly conserved structure and involves in more than sixty cofactors for catalyzing C-, S- and N-related oxygen transfer reactions. Since oxygen atom transfer reactions are featured prominently in energy transduction in today's biology, Mo could have very well catalyzed critical redox reactions for the emergence of life, and the antiquity of Mo in biology is strongly suggested by phylogenic analysis.

For rationally predicting the evolutionary pathway of Mo-S2(pterin) cofactors, I focused on molybdenum sulfide mineral as a prebiotic catalyst for catalyzing oxygen transfer redox reactions and clarified a [MoS4O] species as the key intermediate. Here I will establish a [MoS4O]-based model system for studying the evolution of molybdoenzymes within a metal-ligand-substrate system by integrating electrochemical and spectroscopic methods; further I plan to compare the catalytic activities between MoS4O and WS4O clusters and the easiness/tendency for evolution. The critical factors which determine the elemental selection for catalysis (that is, which element and ligand environment are critical for catalysis) will be derived for screening prebiotic catalysts for specific substrates.