Halotolerant cyanobacterium Aphanothece halophytica contains an Na(+)/H(+) antiporter, homologous to eukaryotic ones, with novel ion specificity affected by C-terminal tail.
Recently, a cyanobacterium Synechocystis sp. PCC 6803 has been shown to contain an Na(+)/H(+) antiporter gene homologous to plants (SOS1 and AtNHX1 from Arabidopsis) and mammalians (NHEs from human) but not to Escherichia coli (nhaA and nhaB). Here, we examined whether a halotolerant cyanobacterium Aphanothece halophytica has homologous genes. It turned out that A. halophytica contains an Na(+)/H(+) antiporter homologous to plants, mammalians, and some bacteria (nhaP from Pseudomonas and synnhaP from Synechocystis) but with novel ion specificity. Its gene product, ApNhaP (Na(+)/H(+) antiporter from Aphanothece halophytica), exhibited the Na(+)/H(+) antiporter activity over a wide pH range between 5 and 9 and complemented the Na(+)-sensitive phenotype of the antiporter-deficient E. coli mutant. The ApNhaP had virtually no activity for the Li(+)/H(+) antiporter but showed high Ca(2+)/H(+) antiporter activity at alkaline pH. The ApNhaP complemented the Ca(2+)-sensitive phenotype of the E. coli mutant but not the Li(+)-sensitive phenotype. The replacement of a long C-terminal tail of ApNhaP with that of Synechocystis altered the ion specificity of the antiporter. These results suggest that the ion specificity of an Na(+)/H(+) antiporter is partly determined by the structural properties of the C-terminal tail, which was well exemplified in the case of A. halophytica.
Waditee
R
R
Research Institute, Faculty of Science and Technology, Meijo University, Nagoya 468-8502, Japan.
Hibino
T
T
Tanaka
Y
Y
Nakamura
T
T
Incharoensakdi
A
A
Takabe
T
T
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000032:analysis; D004926:Escherichia coli / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008094:Lithium / Q000378:metabolism; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D012965:Sodium Chloride / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D017923:Sodium-Hydrogen Exchangers; D012965:Sodium Chloride; D008094:Lithium; D002118:Calcium