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J. Biol. Chem., Vol. 281, Issue 36, 26552-26561, September 8, 2006

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The Structural and Functional Units of Heteromeric Amino Acid Transporters

THE HEAVY SUBUNIT rBAT DICTATES OLIGOMERIZATION OF THE HETEROMERIC AMINO ACID TRANSPORTERS^*

Esperanza Fernández¹², Maite Jiménez-Vidal¹³, María Calvo, Antonio Zorzano, Francesc Tebar, Manuel Palacín⁴⁵, and Josep Chillarón⁴⁶

From the Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona and Institute for Research in Biomedicine, Barcelona Science Park, E-08028 Barcelona, Spain and Departament de Biologia Cellular, Institut d'Investigacions Biomèdiques August Pi i Sunyer, Facultat de Medicina, Universitat de Barcelona, 08036 Barcelona, Spain

Heteromeric amino acid transporters are composed of a catalytic light subunit and a heavy subunit linked by a disulfide bridge. We analyzed the structural and functional units of systems b^0,+ and x ^-_C, formed by the heterodimers b^0,+AT-rBAT and xCT-4F2hc, respectively. Blue Native gel electrophoresis, cross-linking, and fluorescence resonance energy transfer in vivo indicate that system b^0,+ is a heterotetramer [b^0,+AT-rBAT]₂, whereas xCT-4F2hc seems not to stably or efficiently oligomerize. However, substitution of the heavy subunit 4F2hc for rBAT was sufficient to form a heterotetrameric [xCT-rBAT]₂ structure. The functional expression of concatamers of two light subunits (which differ only in their sensitivity to inactivation by a sulfhydryl reagent) suggests that a single heterodimer is the functional unit of systems b^0,+ and x ^-_C.

Received for publication, April 27, 2006 , and in revised form, June 27, 2006.

^* This study was supported in part by Spanish Ministry of Science and Technology Grant SAF2003-08940 (to M. P.), by Institut de Salud Carlos III networks C3/08P and G03/054 (to M. P.), and by Generalitat de Catalunya Grant 2005 SGR00947. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental material.

¹ These authors contributed equally to this study and share first authorship.

² Supported by a postdoctoral contract from the Comissionat per a Universitats i Recerca.

³ Supported by the BIOMED BMH4 CT98-3514.

⁴ These authors contributed equally to this study and share last authorship.

⁵ To whom correspondence may be addressed: IRB-PCB, Barcelona Science Park, Josep Samitier 1-5, 08028, and Dept. of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Av. Diagonal, 645, E-08028, Barcelona, Spain. Tel.: 34-934034617 and 34-934034700; Fax: 34 934034717; E-mail: mpalacin{at}pcb.ub.es.

⁶ A senior researcher from the Programa Ramón y Cajal of the Spanish Ministry of Science and Technology. To whom correspondence may be addressed: IRB-PCB, Barcelona Science Park, Josep Samitier 1-5, 08028, and Dept. of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Av. Diagonal, 645, E-08028, Barcelona, Spain. Tel.: 34-934034617 and 34-934034700; Fax: 34-934034717; E-mail: jchillaron{at}ub.edu.

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