Characterization of Two Na(K, Li)/H Antiporters from .

The Na/H antiporter NhaC family protein is a kind of Na/H exchanger from the ion transporter (IT) superfamily, which has mainly been identified in the halophilic bacteria of . However, little is known about the Na/H antiporter NhaC family of proteins in the extremely halophilic archaea. In this study, two Na/H antiporter genes, and , were screened from the genome of based on the gene library and complementation of salt-sensitive KNabc. A clone vector pUC18 containing or could make KNabc tolerate 0.6 M/0.7 M NaCl or 30 mM/40 mM LiCl and a pH of up to 8.5/9.5, respectively. Functional analysis shows that the Na(K, Li)/H antiport activities of NhaC1 and NhaC2 are both pH-dependent in the range of pH 7.0-10.0, and the optimal pH is 9.5. Phylogenetic analysis shows that both NhaC1 and NhaC2 belong to the Na/H antiporter NhaC family of proteins and are significantly distant from the identified NhaC proteins from . In summary, we have identified two Na(K, Li)/H antiporters from .