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Cyanobacteria use the carbon dioxide(CO2)concentrating mechanism(CCM)for efficient intracellular accumulation of inorganic carbon(Ci)under limited CO2growth conditions.This mechanism vastly improves the Ci uptake efficiency compared to what would occur based only on the RubisCO kinetic properties.The Ci is mainly acquired from bicarbonate(HCO3-)or from the conversion of dissolved CO2to HCO3-.The LysR-type transcriptional regulator(LTTR)CmpR protein,promotes the expression of HCO3-transporter in Synechococcus elongatus strain PCC7942by activating the cmpABCD operon under Ci-limiting conditions.Moreover,the CmpR requires a metabolic effector to control the transcriptional activity of the cmp operon.Ribulose-1,5-bisphosphate(RuBP)has been reported to improve the binding of CmpR to the regulatory region of the cmp operon for inducing the HCO3-transporter expression.Previous studies have evoked the binding of the RuBP to CmpR protein,but lacking direct structural evidence.The structural representation of RuBP attached to the effector-binding domain(EBD)of CmpR was never been reported;thus raising numerous questions about the exact RuBP binding site and the residues involved in this binding.Therefore,obtaining the complex CmpR-EBD-RuBP is a major scientific advance.This dissertation reports the structure of CmpR-EBD in complex with the co-activator RuBP.Furthermore,we found that the RuBP bound to CmpR-EBD with distinct binding pattern compared to what was previously reported in LTTRs.These findings provide structural and biochemical insights into the LysR-type protein family and may be considered as a start-point for the future study of the structure-based regulation mechanism and the physiological functions of CbbRs.