Glutamate 85 is involved in the sodium/proton exchange activity of the Escherichia coli ChaA

Metagenomic cloning and characterization of Na⁺/H⁺ antiporter genes taken from sediments in Chaerhan Salt Lake in China

A metagenomic library containing 8,000 clones was constructed by using genomic DNA obtained from Chaerhan Salt Lake in northwest China. Three Na(+)/H(+) antiporters, C4-NhaG, C47-NhaG and C49-NhaG that grouped to the NhaG family, were screened and cloned from this metagenome by complementing Escherichia coli strain KNabc (ΔnhaA ΔnhaB ΔchaA) in medium containing 0.2 M NaCl. The three putative Na(+)/H(+) antiporters were membrane proteins with 10, 11 and 11 transmembrane segments, respectively. They enabled E. coli KNabc to grow in medium containing 0.2-0.6 M Na(+) or 7-14 mM Li(+). Everted membrane vesicles prepared from E. coli KNabc cells carrying C49-NhaG exhibited Na(+)/H(+) and Li(+)/H(+) antiport activities.