title: A novel role of the C-terminus of b 0,+ AT in the ER-Golgi trafficking of the rBAT-b 0,+ AT heterodimeric amino acid transporter.
abstract: The heterodimeric complex composed of rBAT (related to b(0,+) amino acid transporter), a single-membrane-spanning glycosylated heavy chain, and b(0,+)AT, a putative 12-membrane-spanning non-glycosylated light chain, is an amino acid transporter that mediates the activity of system b(0,+), a major apical transport system for cystine and dibasic amino acids in renal proximal tubule and small intestine. The C-terminus of b(0,+)AT has been proposed to play an important role in the functional expression of the heterodimeric transporters. In the present study, to reveal the roles of the C-terminus, we analysed b(0,+)AT mutants whose C-termini were sequentially deleted or replaced by site-directed mutagenesis in polarized MDCKII (Madin-Darby canine kidney II), non-polarized HEK-293 (human embryonic kidney-293) and HeLa cells. Although the deletion of C-terminus of b(0,+)AT did not affect the formation of a heterodimer with rBAT, it resulted in the loss of apparent transport function, owing to the failure of the plasma-membrane targeting of rBAT-b(0,+)AT heterodimeric complex associated with incomplete glycosylation of rBAT. A motif-like sequence Val(480)-Pro(481)-Pro(482) was identified in the C-terminus of b(0,+)AT to be responsible for the C-terminus action in promoting the trafficking of rBAT-b(0,+)AT heterodimeric complex from the ER (endoplasmic reticulum) to Golgi apparatus. This is, to our knowledge, the first demonstration of the active contribution of the C-terminus of a light-chain subunit to the intracellular trafficking of heterodimeric transporters. Because the motif-like sequence Val(480)-Pro(481)-Pro(482) is well conserved among the C-termini of light-chain subunits, common regulatory mechanisms could be proposed among heterodimeric amino acid transporters.
authors.affiliation: Department of Pharmacology and Toxicology, Kyorin University School of Medicine, Tokyo, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Sakamoto
authors.forename: Arthit
authors.initials: A
authors.lastname: Chairoungdua
authors.forename: Shushi
authors.initials: S
authors.lastname: Nagamori
authors.forename: Pattama
authors.initials: P
authors.lastname: Wiriyasermkul
authors.forename: Kanyarat
authors.initials: K
authors.lastname: Promchan
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Tanaka
authors.forename: Toru
authors.initials: T
authors.lastname: Kimura
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ueda
authors.forename: Masaaki
authors.initials: M
authors.lastname: Fujimura
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Shigeta
authors.forename: Yukio
authors.initials: Y
authors.lastname: Naya
authors.forename: Koichiro
authors.initials: K
authors.lastname: Akakura
authors.forename: Haruo
authors.initials: H
authors.lastname: Ito
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Endou
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Ichikawa
authors.forename: Yoshikatsu
authors.initials: Y
authors.lastname: Kanai
mesh_terms: D000595:Amino Acid Sequence; D026905:Amino Acid Transport Systems / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D017353:Gene Deletion; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D055503:Protein Multimerization; D021381:Protein Transport; D016415:Sequence Alignment
chemical_list: D026905:Amino Acid Transport Systems