title: Carboxyl-terminal hydrophilic tail of a NhaP type Na+/H+ antiporter from cyanobacteria is involved in the apparent affinity for Na+ and pH sensitivity.
abstract: Little information is available on the C-terminal hydrophilic tails of prokaryotic Na(+)/H(+) antiporters. To address functional properties of the C-terminal tail, truncation mutants in this domain were constructed. Truncation of C-terminal amino acid residues of NhaP1 type antiporter from Synechocystis PCC6803 (SynNhaP1) did not change the V(max) values, but increased the K(m) values for Na(+) and Li(+) about 3 to 15-fold. Truncation of C-terminal tail of a halotolerant cyanobacterium Aphanothece halophytica (ApNhaP1) significantly decreased the V(max) although it did not alter the K(m) values for Na(+). The C-terminal part of SynNhaP1 was expressed in E. coli and purified as a 16kDa soluble protein. Addition of purified polypeptide to the membrane vesicles expressing the C-terminal truncated SynNhaP1 increased the exchange activities. Change of Glu519 and Glu521 to Lys in C-terminal tail altered the pH dependence of Na(+)/H(+) and Li(+)/H(+) exchange activities. These results indicate that the specific acidic amino acid residues at C-terminal domain play important roles for the K(m) and the pH dependence of the exchange activity.
authors.affiliation: Research Institute of Meijo University, Nagoya 468-8502, Japan.
authors.forename: Rungaroon
authors.initials: R
authors.lastname: Waditee
authors.forename: Teerapong
authors.initials: T
authors.lastname: Buaboocha
authors.forename: Mariko
authors.initials: M
authors.lastname: Kato
authors.forename: Takashi
authors.initials: T
authors.lastname: Hibino
authors.forename: Shigetoshi
authors.initials: S
authors.lastname: Suzuki
authors.forename: Tatsunosuke
authors.initials: T
authors.lastname: Nakamura
authors.forename: Teruhiro
authors.initials: T
authors.lastname: Takabe
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D017384:Sequence Deletion; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D046939:Synechocystis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D017923:Sodium-Hydrogen Exchangers