title: Structural implications of the EL(KIQ)(L/C)LD(A/G)DD sequence in the C-terminal cytoplasmic tail for proper targeting of anion exchanger 1 to the plasma membrane.
abstract: While the C-terminal cytoplasmic tail of anion exchanger 1 (AE1, band 3) has been reported to possess important physiological roles, including one for proper membrane trafficking, its precise characteristics remain unclear. To clarify the overall structural consequences of the conserved sequence EL(K/Q)(L/C)LD(A/G)DD, containing the core binding sequence LDADD for carbonic anhydrase II, in the C-terminal region, we analyzed the membrane expression and turnover of bovine AE1 with a series of truncation and substitution mutations in HEK293 cells. Immunofluorescence microscopy and cell-surface biotinylation demonstrated that truncation mutants missing 18 C-terminal residues targeted the plasma membrane, but the one lacking the conserved region, by truncation of 28 amino acid residues, was retained inside the cells. Substitutions of Ala for Glu901, Leu902, Leu905, and Asp906 in the sequence E901L(K/Q)(L/C)LDADD909 of bovine AE1 or those in the corresponding murine sequence also caused intracellular retention, though these mutants had half-lives comparable to that for wild-type AE1. These data demonstrate that the conserved amino acid residues Glu1, Leu2, Leu5, and Asp6 in the EL(K/Q)(L/C)LD(A/G)DD region have essential structural consequences in stable expression of AE1 at the plasma membrane regardless of the ability in binding to carbonic anhydrase II of this region.
authors.affiliation: Laboratory of Molecular Medicine, Department of Veterinary Clinical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan. inazo@vetmed.hokudai.ac.jp
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Adachi
authors.forename: Daisuke
authors.initials: D
authors.lastname: Ito
authors.forename: Takao
authors.initials: T
authors.lastname: Kurooka
authors.forename: Yayoi
authors.initials: Y
authors.lastname: Otsuka
authors.forename: Nobuto
authors.initials: N
authors.lastname: Arashiki
authors.forename: Kota
authors.initials: K
authors.lastname: Sato
authors.forename: Mutsumi
authors.initials: M
authors.lastname: Inaba
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001457:Anion Exchange Protein 1, Erythrocyte / Q000737:chemistry* / Q000378:metabolism*; D002417:Cattle; D002460:Cell Line; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary
chemical_list: D001457:Anion Exchange Protein 1, Erythrocyte