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Molecular and Cellular Biology, December 2008, p. 7514-7531, Vol. 28, No. 24
0270-7306/08/$08.00+0     doi:10.1128/MCB.00946-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Characterization of Human GTPBP3, a GTP-Binding Protein Involved in Mitochondrial tRNA Modification{triangledown} ,{dagger}

Magda Villarroya,1,{ddagger} Silvia Prado,1,{ddagger} Juan M. Esteve,2,{ddagger} Miguel A. Soriano,2,{ddagger} Carmen Aguado,2 David Pérez-Martínez,1,¶ José I. Martínez-Ferrandis,1,|| Lucía Yim,1,§ Victor M. Victor,3 Elvira Cebolla,1 Asunción Montaner,2 Erwin Knecht,2,{dagger}{dagger} and M.-Eugenia Armengod1,{dagger}{dagger}*

Laboratorio de Genética Molecular,1 Laboratorio de Biología Celular and CIBER de Enfermedades Raras, Centro de Investigación Príncipe Felipe, Avenida Autopista del Saler, 16-3, 46012 Valencia, Spain,2 Hospital Universitario Dr. Peset, Avenida Gaspar Aguilar, 90, 46017 Valencia, Spain3

Received 13 June 2008/ Returned for modification 18 July 2008/ Accepted 2 October 2008

Human GTPBP3 is an evolutionarily conserved, multidomain protein involved in mitochondrial tRNA modification. Characterization of its biochemical properties and the phenotype conferred by GTPBP3 inactivation is crucial to understanding the role of this protein in tRNA maturation and its effects on mitochondrial respiration. We show that the two most abundant GTPBP3 isoforms exhibit moderate affinity for guanine nucleotides like their bacterial homologue, MnmE, although they hydrolyze GTP at a 100-fold lower rate. This suggests that regulation of the GTPase activity, essential for the tRNA modification function of MnmE, is different in GTPBP3. In fact, potassium-induced dimerization of the G domain leads to stimulation of the GTPase activity in MnmE but not in GTPBP3. The GTPBP3 N-terminal domain mediates a potassium-independent dimerization, which appears as an evolutionarily conserved property of the protein family, probably related to the construction of the binding site for the one-carbon-unit donor in the modification reaction. Partial inactivation of GTPBP3 by small interfering RNA reduces oxygen consumption, ATP production, and mitochondrial protein synthesis, while the degradation of these proteins slightly increases. It also results in mitochondria with defective membrane potential and increased superoxide levels. These phenotypic traits suggest that GTPBP3 defects contribute to the pathogenesis of some oxidative phosphorylation diseases.

* Corresponding author. Mailing address: Laboratorio de Genética Molecular, Centro de Investigación Príncipe Felipe, Avenida Autopista del Saler, 16-3, 46012 Valencia, Spain. Phone: 34 963289680. Fax: 34 963289701. E-mail: armengod{at}cipf.es

{triangledown} Published ahead of print on 13 October 2008.

{dagger} Supplemental material for this article may be found at http://mcb.asm.org/.

{ddagger} M.V., S.P., J.M.E., and M.A.S. contributed equally to this work.

Present address: Experimental Therapeutics, Wellcome Trust Brenner Building, St. James's University Hospital, Leeds, West Yorkshire LS9 7TF, United Kingdom.

|| Present address: Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461.

§ Present address: Instituto de Higiene, Facultad de Medicina, Universidad de la República, Avda. Alfredo Navarro 3051, 11600 Montevideo, Uruguay.

{dagger}{dagger} Senior authors E.K. and M.-E.A. contributed equally to this work.

Molecular and Cellular Biology, December 2008, p. 7514-7531, Vol. 28, No. 24
0270-7306/08/$08.00+0     doi:10.1128/MCB.00946-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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