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  • The EMBO Journal (2002) 21, 4906 - 4914
  • doi:10.1093/emboj/cdf500

The light subunit of system bo,+ is fully functional in the absence of the heavy subunit

Núria Reig1, Josep Chillarón1, Paola Bartoccioni1, Esperanza Fernández1, Annie Bendahan2, Antonio Zorzano1, Baruch Kanner2, Manuel Palacín1 and Joan Bertran1

  1. Departament de Bioquimica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Avda Diagonal 645, Barcelona E-08028, Spain
  2. Department of Biochemistry, The Hebrew University Hadassah Medical School, PO Box 12272, Jerusalem 91120, Israel

Correspondence to:

Manuel Palacín, E-mail: mpalacin@bio.ub.es

Joan Bertran, E-mail: comulada@bio.ub.es

Received 25 March 2002; Accepted 31 July 2002; Revised 10 July 2002

The heteromeric amino acid transporters are composed of a type II glycoprotein and a non-glycosylated polytopic membrane protein. System bo,+ exchanges dibasic for neutral amino acids. It is composed of rBAT and bo,+AT, the latter being the polytopic membrane subunit. Mutations in either of them cause malfunction of the system, leading to cystinuria. bo,+AT-reconstituted systems from HeLa or MDCK cells catalysed transport of arginine that was totally dependent on the presence of one of the bo,+ substrates inside the liposomes. rBAT was essential for the cell surface expression of bo,+AT, but it was not required for reconstituted bo,+AT transport activity. No system bo,+ transport was detected in liposomes derived from cells expressing rBAT alone. The reconstituted bo,+AT showed kinetic asymmetry. Expressing the cystinuria-specific mutant A354T of bo,+AT in HeLa cells together with rBAT resulted in defective arginine uptake in whole cells, which was paralleled by the reconstituted bo,+AT activity. Thus, subunit bo,+AT by itself is sufficient to catalyse transmembrane amino acid exchange. The polytopic subunits may also be the catalytic part in other heteromeric transporters.

  • Keywords:

    • bo,+AT–rBAT exchanger,
    • bo,+AT reconstitution,
    • cystinuria,
    • transport asymmetry,
    • reabsorption