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Project Progress

Progress has continued towards understanding the novel gamma-class carbonic anhydrase thought to have contributed to the metabolism of ancient thermophilic and autotrophic methanoarchaea. The active site of the enzyme from Methanosarcina thermophila has been characterized in an effort to understand the evolution of this class and the physiological function in the cell. Insights into the mechanism of proton transfer suggest a role for bicarbonate. A role for the active site Arg 59 in catalysis has been established. Parallel investigations to understand the beta-class carbonic anhydrase from the thermophilic and autotrophic archaeon Methanobacterium thermoautotrophicum have also revealed features of the active site that contribute to understanding of the evolution of this class and the catalytic mechanism with applications to the physiological function. An active site aspartate residue has been implicated in proton transport, and an active site arginine in the carbon dioxide hydration step of catalysis. Finally, analysis of the genomic sequence of Methanosarcina acetivorans has provided a foundation for genomic and proteomic approaches to discover still other novel proteins and enzymes that further our understanding of how the methanogenic Archaea contributed to the origin and early evolution of life on earth. The results identify numerous open reading frames (ORFs) with postulated functions in ancient pathways. Over expression of these ORFs and characterization of the gene products are expected to identify new metabolic capabilities, possibly of ancient origin.