title: Functional role of arginine 425 in the mammalian Na⁺/H⁺ exchanger.
abstract: Na(+)/H(+) exchanger isoform 1 (NHE1) is the principal plasma membrane Na(+)/H(+) exchanger of mammalian cells and functions by exchanging one intracellular proton for one extracellular sodium ion. Critical transmembrane segments of Na(+)/H(+) exchangers have discontinuous transmembrane helices, which result in a dipole within the membrane. Amino acid R425 has been suggested to play an important role in neutralizing one such helix dipole. To investigate this hypothesis, R425 was mutated to alanine, glutamine, histidine, or lysine and the mutant NHE1 proteins were expressed and characterized in NHE1-deficient cells. The R425A and R425E mutants exhibited complete loss of expression of mature, fully glycosylated NHE1, reduced expression overall, and greatly reduced cell surface targeting. The cell surface targeting, expression, and activity of the R425H and R425K mutant proteins were also impaired, though residual NHE1 activity remained. When reduced targeting and expression were accounted for, the R425H and R425K mutant proteins had activity similar to that of the wild-type protein. The results suggest that R425 is critical for NHE1 expression, targeting, and activity and that replacement with another basic residue can rescue activity. The findings are consistent with a role for R425 in both neutralizing a helix dipole and maintaining NHE1 structure and function.
authors.affiliation: Department of Biochemistry, University of Alberta, 347 Medical Sciences Building, Edmonton, AB T6G 2H7, Canada.
authors.forename: Xiuju
authors.initials: X
authors.lastname: Li
authors.forename: Yike
authors.initials: Y
authors.lastname: Ma
authors.forename: Larry
authors.initials: L
authors.lastname: Fliegel
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001120:Arginine / Q000235:genetics / Q000378:metabolism; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D006224:Cricetinae; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D020125:Mutation, Missense; D017433:Protein Structure, Secondary; D021381:Protein Transport / Q000502:physiology; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D027682:Cation Transport Proteins; C490998:SLC9A1 protein, human; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; D001120:Arginine
keywords: Na+/H+ exchanger; dipôle de l’hélice; helix dipole; pH regulation; régulation du pH; segment transmembranaire; transmembrane segment; échangeur Na+/H+