ABSTRACTNa+-translocating NADH: quinone oxidoreductase (NQR) is a protein complex that exists in the respiratory chain of Vibrio cholerae.... Show moreABSTRACTNa+-translocating NADH: quinone oxidoreductase (NQR) is a protein complex that exists in the respiratory chain of Vibrio cholerae. This complex can transport sodium ions to the outside of the plasma membrane. NQR has important influences on the survival and pathogenesis of V. cholerae. Two of the subunits of NQR, NqrC and NqrB, has a covalently bound FMN coenzyme. This FMN is necessary for the activity of NQR complex. A protein, alternative pyrimidine biosynthesis protein (ApbE) can transfer the FMN molecule to NqrB and NqrC covalently. And ApbE is also important to some other flavoproteins like the NOS and RNF. The ApbE protein use the FAD as the substrate to transfer the FMN group to the NqrC and NqrB apo-enzyme. Mg2+ is necessary for the activity of ApbE protein. Sodium and potassium ion are not necessary, but potassium ion can increase the activity of the ApbE by about ten times. In order to understand the mechanism of potassium activation of ApbE, several potassium binding sites were identified by molecular docking in this study. Point mutations of the amino acid residues constituting these sites were performed. The FMN transfer activity and affinity to potassium ions of these mutants were measured. The results suggest that when G125 was mutated, the binding of potassium ions was affected. Therefore, the structure composed of P126 and G125 may play a significant role in the activation of ApbE potassium ions. Show less
