Analysis on molecular mechanisms of pH-dependent regulation of VaNhaBfrom Vibrio alginolyticus.

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We have conducted a series of domain swapping analysis between pH-sensitive NhaB-like antiporter from Vibrio alginolyticus (VaNhaB) and pH-insensitive NhaB-like antiporter from Escherichia coli (EcNhaB) in order to identify domains or regions that play critical roles in the pH-sensitivity of VaNhaB. Our results revealed the significant importance of the E373-D434 region of VaNhaB in the pH-dependent regulation of its Na+/H+ antiport activity. Furthermore, we demonstrated that E373-D434 region of VaNhaB was able to confer some degree of pH-sensitivity on our pH-insensitive chimeric antiporters that is mainly composed of EcNhaB except for first seven amino acid residues from N-terminal end, which strongly suggest that this region is able to act, at least partially, as a machinery that modifies the activity of NhaB-like antiporter in a pH-dependent manner.