Tuesday, July 31, 2007 - 1:30 PM
S108
Multiple NiFe-Hydrogenases in the Hyperthermophile Pyrococcus furiosus
Francis E. Jenney Jr., Robert C. Hopkins, Ting Li, Junsong Sun, and Michael W.W. Adams. Biochemistry & Molecular Biology, University of Georgia, B222A Davison Life Sciences Complex, Green St., Athens, GA 30602
Pyrococcus furiosus is a member of the domain Archaea, and is a sulfur-independent strictly anaerobic hyperthermophile which is found in surface solfataras. P. furiosus grows heterotrophically utilizing either carbohydrates such as maltose or cellobiose, or peptides as carbon/energy sources, producing organic acids and (in the absence of elemental sulfur) H2. P. furiosus does apparently prefer sulfur as a terminal electron acceptor as it will immediately reduce transcription of hydrogenase-encoding genes, and switch to producing H2S in place of H2 when S° is added to growing cells. There are three Ni-Fe type hydrogenases expressed in the absence of elemental sulfur, two soluble, cytoplasmic enzymes (SHI and SHII), each with four subunits, and one membrane-bound hydrogenase (MBH) of unknown stoichiometry but encoded by an operon of 14 genes. The in vivo roles of the two soluble enzymes are not clear, though based on in vitro studies they appear to act as H2 uptake enzymes, perhaps to recycle electrons from H2 to reduce NADP. The MBH plays a role in energy conservation, creating a proton gradient driven by oxidation of ferredoxin produced by metabolism. The goal of the current research is to elucidate the mechanisms of assembly, and the in vivo metabolic function of these three enzyme complexes. Further, as part of the DOE-funded hydrogen energy initiative, the goal is heterologous expression of functional P. furiosus hydrogenase in Escherichia coli, and ultimately to create a ‘minimal’ form of the enzyme by deletion and mutation.