Halotolerant Cyanobacterium Aphanothece halophyticaContains an Na+/H+ Antiporter, Homologous to Eukaryotic Ones, with Novel Ion Specificity Affected by C-terminal Tail

Abstract

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 Cterminal 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.

Overexpression of a Na + /H + antiporter confers salt tolerance on a freshwater cyanobacterium, making it capable of growth in sea water

“…However, the expression of a Na ϩ ͞H ϩ antiporter from Vibrio alginolytica NhaAv resulted in a Na ϩ -sensitive transformant (16). Recently, we isolated a eukaryotic Na ϩ ͞H ϩ antiporter gene (apnhaP) from a halotolerant cyanobacterium Aphanothece halophytica and showed that ApNhaP exhibits high Na ϩ ͞H ϩ exchange activity over a wide range of pH with novel ion specificity (17). Therefore, it was interesting to examine the effects of expression of ApNhaP and genes for the synthesis of betaine, catalase, and a chaperone (DnaK) and their combinations.…”

Topological analysis of a plant vacuolar Na + /H + antiporter reveals a luminal C terminus that regulates antiporter cation selectivity

“…It has been shown that the activity of H ϩ -coupled antiporters can be affected by modifications at the C or N terminus (29)(30)(31)(32). To test whether the C or N terminus of AtNHX1 plays a role in regulating antiporter activity, we measured the H ϩ -coupled cation transport activity in vacuoles containing the full length AtNHX1 and the N or C terminus truncated forms of AtNHX1 (Fig.…”

Isolation and Functional Characterization ofN-Methyltransferases That Catalyze Betaine Synthesis from Glycine in a Halotolerant Photosynthetic Organism Aphanothece halophytica

“…A. halophytica DnaK has been shown to contain the longer C-terminal segment than other DnaK/Hsp70 family members (21) and exhibit extremely high protein folding activity at high salinity (22). It was also shown that A. halophytica Na ϩ /H ϩ antiporter has novel ion specificity (23) and could confer the tolerance for salt stress of fresh water cyanobacterium capable of growing in sea water (24). Here, we show that in contrast to other oxygenevolving photosynthetic organisms, A. halophytica synthesizes betaine from glycine by a three-step methylation.…”

“…Homology searches were made using the BLAST program as previously described (23). Two methyltransferase genes, ORF1 and ORF2, homologous to EcGSMT and EcSDMT were found and amplified by the PCR reactions using the genomic DNA of A. halophytica as a template.…”