Carboxyl-terminal hydrophilic tail of a NhaP type Na+/H+ antiporter from cyanobacteria is involved in the apparent affinity for Na+ and pH sensitivity.
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.
Waditee
Rungaroon
R
Research Institute of Meijo University, Nagoya 468-8502, Japan.
Buaboocha
Teerapong
T
Kato
Mariko
M
Hibino
Takashi
T
Suzuki
Shigetoshi
S
Nakamura
Tatsunosuke
T
Takabe
Teruhiro
T
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
D001426:Bacterial Proteins; D017923:Sodium-Hydrogen Exchangers