One major objective is to elucidate fundamental relationships between the structure and function of the enzyme ribulose bisphosphate carboxyase/oxygenase (RuBisCO) which catalyzes primary carbon dioxide fixation in Nature and is one of the most abundant proteins on earth. This protein, which consists of large (L) and small (S) subunits in most species, undergoes carbamylation to a catalytically active form which can then catalyze either carboxylative or oxygenolytic cleavage of ribulose bisphosphate. The latter initiates photorespiration, a process which opposes growth on carbon dioxide. The long-range objective is to test the feasibility of enhancing photosynthesis and/or decreasing photorespiration by altering RuBisCO. Attendant changes in autotrophic growth rate may be striking and may ultimately be reflected in increased plant productivity. The emphasis for many years in this laboratory has been on RuBisCO from bacteria. Bacteria not only provide enzymes that vary in quaternary structure (some lacking the S subunit) but some are excellent modils for the plant enzyme. A better understanding of the structure and function of proteins (such as RuBisCO) may assist in the cure or arrest of human diseases which are frequently due to the production of altered proteins. In the current project period, it has been discovered that RuBisCO is anchored to the cytoplasmic membrane via S subunits in one photosynthetic bacterium. The biological significance of this attachment will be investigated. More specifically the structure and function of RuBisCO will be investigated in terms of: (a) the function of S subunits including the domain(s) for membrane attachment and (b) the function of L subunits. These investigations will include chemical cross-linking studies and in vitro mutagenesis of L and S subunit genes and will focus on one of the cyanobacteria, Anacystis nidulans. They will also include studies of the modification of RuBisCO by transglutaminase to assess the biological significance of this modification. Parallel studies of the replication of foreign DNA in cyanobacteria will be conducted. Hence, the feasibility of incorporating interesting genes (such as L and S subunit gene modifications) into cyanobacteria will be examined. Results will shed light on the origin of DNA replication in cyanobacteria and provide a basis for comparison with other bacteria including pathogens.
