title: The light subunit of system b(o,+) is fully functional in the absence of the heavy subunit.
abstract: The heteromeric amino acid transporters are composed of a type II glycoprotein and a non-glycosylated polytopic membrane protein. System b(o,+) exchanges dibasic for neutral amino acids. It is composed of rBAT and b(o,+)AT, the latter being the polytopic membrane subunit. Mutations in either of them cause malfunction of the system, leading to cystinuria. b(o,+)AT-reconstituted systems from HeLa or MDCK cells catalysed transport of arginine that was totally dependent on the presence of one of the b(o,+) substrates inside the liposomes. rBAT was essential for the cell surface expression of b(o,+)AT, but it was not required for reconstituted b(o,+)AT transport activity. No system b(o,+) transport was detected in liposomes derived from cells expressing rBAT alone. The reconstituted b(o,+)AT showed kinetic asymmetry. Expressing the cystinuria-specific mutant A354T of b(o,+)AT in HeLa cells together with rBAT resulted in defective arginine uptake in whole cells, which was paralleled by the reconstituted b(o,+)AT activity. Thus, subunit b(o,+)AT by itself is sufficient to catalyse transmembrane amino acid exchange. The polytopic subunits may also be the catalytic part in other heteromeric transporters.
authors.affiliation: Departament de Bioquimica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Avda Diagonal 645, Barcelona E-08028, Spain.
authors.forename: Núria
authors.initials: N
authors.lastname: Reig
authors.forename: Josep
authors.initials: J
authors.lastname: Chillarón
authors.forename: Paola
authors.initials: P
authors.lastname: Bartoccioni
authors.forename: Esperanza
authors.initials: E
authors.lastname: Fernández
authors.forename: Annie
authors.initials: A
authors.lastname: Bendahan
authors.forename: Antonio
authors.initials: A
authors.lastname: Zorzano
authors.forename: Baruch
authors.initials: B
authors.lastname: Kanner
authors.forename: Manuel
authors.initials: M
authors.lastname: Palacín
authors.forename: Joan
authors.initials: J
authors.lastname: Bertran
mesh_terms: D026905:Amino Acid Transport Systems / Q000235:genetics / Q000502:physiology*; D026923:Amino Acid Transport Systems, Basic; D000818:Animals; D001120:Arginine / Q000378:metabolism; D001692:Biological Transport / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D003553:Cystine / Q000378:metabolism; D003555:Cystinuria / Q000235:genetics; D004285:Dogs; D006367:HeLa Cells; D006801:Humans; D007668:Kidney / Q000166:cytology; D007930:Leucine / Q000378:metabolism; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits
chemical_list: D026905:Amino Acid Transport Systems; D026923:Amino Acid Transport Systems, Basic; D002352:Carrier Proteins; D008081:Liposomes; D008562:Membrane Glycoproteins; D021122:Protein Subunits; C499489:SLC7A9 protein, human; D003553:Cystine; D001120:Arginine; D007930:Leucine