Specificity/Regulation of Cyanobacterial ABC Transporters

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DESCRIPTION (provided by applicant): The build-up of greenhouse gases in our atmosphere has, and will continue to, lead to a steady increase in the global temperature. A way to halt the further atmospheric accumulation of greenhouses gases, particularly carbon dioxide, is through manipulation of the natural carbon-sequestering mechanisms of aquatic cyanobacteria. One significant factor limiting carbon sequestration in these organisms is the low bioavailability of iron. For the acquisition of bicarbonate and iron, cyanobacteria employ high-affinity ATP-binding cassette (ABC) transporters. These ABC transporters are composed of a periplasmic solute-binding lipoprotein, a cytoplasmic-membrane spanning permease, and an ATPase that powers solute transport. A combination of x-ray crystallography, biochemical and molecular biology techniques will be used to examine both the molecular basis of substrate specificity and transport regulation in the bicarbonate CmpABCD, and the ferric iron FutABC transporters of Synechocystis sp PCC 6803. X-ray crystal structures of the CmpA, CmpC and CmpD proteins will be pursued, as well as a biochemical characterization of the unique multi-domain CmpC protein that is involved in the regulation of bicarbonate uptake. Both thermodynamic and enzymatic techniques will be employed to investigate the interactions between the ATPase domains of CmpC and CmpD. The FutABC transporter will be used to ask the question of whether the membrane permease and ATPase components of ABC transporters plays a role in solute recognition. The solute-binding specificity of the ferric-binding protein FutA1 will be altered in order to test whether the FutBC machinery can accept alternate metal ions. These experiments will involve genetic manipulation of Synechocystis for the purpose of testing metal ion acquisition through FutBC.