Structural Study Of Synechococcus Elongatus CmpR Effector Binding Domain In Complex With Ribulose-1,5-bisphosphate

Cyanobacteria use the carbon dioxide?CO₂?concentrating mechanism?CCM?for efficient intracellular accumulation of inorganic carbon?Ci?under limited CO₂ growth 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 CO₂ to HCO3-.The LysR-type transcriptional regulator?LTTR?CmpR protein,promotes the expression of HCO3-transporter in Synechococcus elongatus strain PCC 7942 by 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.