title: Differential roles of tryptophan residues in the functional expression of human anion exchanger 1 (AE1, Band 3, SLC4A1).
abstract: Anion exchanger 1 (AE1) is a 95 kDa glycoprotein that facilitates Cl(-)=HCO(-)(3) exchange across the erythrocyte plasma membrane. This transport activity resides in the 52 kDa C-terminal membrane domain (Gly(361)-Val(911)) predicted to span the membrane 14 times. To explore the role of tryptophan (Trp) residues in AE1 function, the seven endogenous Trp residues in the membrane domain were mutated individually to alanine (Ala) and phenylalanine (Phe). Expression levels, cell surface abundance, inhibitor binding and transport activities of the mutants were measured upon expression in HEK-293 cells. The seven Trp residues divided into three classes according the impact of mutations on the functional expression of AE1: Class 1, dramatically decreased expression (Trp(492) and Trp(496)); Class 2, decreased expression by Ala substitution but not Phe (Trp(648), Trp(662) and Trp(723)); and Class 3, normal expression (Trp(831) and Trp(848)). The results indicate that Trp residues play differential roles in AE1 expression and function depending on their location in the protein and that Trp mutants with low expression are misfolded and retained in the endoplasmic reticulum.
authors.affiliation: Department of Biochemistry, University of Toronto , Toronto, Canada and.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Okawa
authors.forename: Jing
authors.initials: J
authors.lastname: Li
authors.forename: Arghya
authors.initials: A
authors.lastname: Basu
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Casey
authors.forename: Reinhart A F
authors.initials: RA
authors.lastname: Reithmeier
mesh_terms: D020816:Amino Acid Motifs; D001457:Anion Exchange Protein 1, Erythrocyte / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D004721:Endoplasmic Reticulum / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D017510:Protein Folding; D021381:Protein Transport; D014364:Tryptophan / Q000235:genetics / Q000378:metabolism*
chemical_list: D001457:Anion Exchange Protein 1, Erythrocyte; C454201:SLC4A1 protein, human; D014364:Tryptophan
keywords: Anion exchanger 1; membrane protein folding; tryptophan mutagenesis