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.
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.
Sakamoto
Shinichi
S
Department of Pharmacology and Toxicology, Kyorin University School of Medicine, Tokyo, Japan.
Chairoungdua
Arthit
A
Nagamori
Shushi
S
Wiriyasermkul
Pattama
P
Promchan
Kanyarat
K
Tanaka
Hidekazu
H
Kimura
Toru
T
Ueda
Takeshi
T
Fujimura
Masaaki
M
Shigeta
Yasuhiro
Y
Naya
Yukio
Y
Akakura
Koichiro
K
Ito
Haruo
H
Endou
Hitoshi
H
Ichikawa
Tomohiko
T
Kanai
Yoshikatsu
Y
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
D026905:Amino Acid Transport Systems