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J. Biol. Chem., Vol. 278, Issue 38, 36169-36175, September 19, 2003

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The Multifunctional Isopropyl Alcohol Dehydrogenase of Phytomonas sp. Could Be the Result of a Horizontal Gene Transfer from a Bacterium to the Trypanosomatid Lineage^*

Sara M. Molinas , Silvia G. Altabe , Fred R. Opperdoes , Mark H. Rider ¶, Paul A. M. Michels  and Antonio D. Uttaro  ||

From the Instituto de Biología Molecular y Celular de Rosario-Consejo Nacional de Investigaciones Científicas y Técnicas, Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, 2000-Rosario, Santa Fe, Argentina and the Research Unit for Tropical Diseases and ^¶Hormone and Metabolic Research Unit, Christian de Duve Institute of Cellular Pathology, Université Catholique de Louvain, ICP-TROP/74.39, Avenue Hippocrate 74, B-1200 Brussels, Belgium

Isopropyl alcohol dehydrogenase (iPDH) is a dimeric mitochondrial alcohol dehydrogenase (ADH), so far detected within the Trypanosomatidae only in the genus Phytomonas. The cloning, sequencing, and heterologous expression of the two gene alleles of the enzyme revealed that it is a zinc-dependent medium-chain ADH. Both polypeptides have 361 amino acids. A mitochondrial targeting sequence was identified. The mature proteins each have 348 amino acids and a calculated molecular mass of 37 kDa. They differ only in one amino acid, which can explain the three isoenzymes and their respective isoelectric points previously found. A phylogenetic analysis locates iPDH within a cluster with fermentative ADHs from bacteria, sharing 74% similarity and 60% identity with Ralstonia eutropha ADH. The characterization of the two bacterially expressed Phytomonas enzymes and the comparison of their kinetic properties with those of the wild-type iPDH and of the R. eutropha ADH strongly support the idea of a horizontal gene transfer event from a bacterium to a trypanosomatid to explain the origin of the iPDH in Phytomonas. Phytomonas iPDH and R. eutropha ADH are able to use a wide range of substrates with similar K_m values such as primary and secondary alcohols, diols, and aldehydes, as well as ketones such as acetone, diacetyl, and acetoin. We speculate that, as for R. eutropha ADH, Phytomonas iPDH acts as a safety valve for the release of excess reducing power.

Received for publication, May 30, 2003

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank^TM/EBI Data Bank with accession number(s) AY283263.

^* This work was supported in part by Fondo Nacional de Ciencia y Tecnología and Secretaría de Ciencia y Tecnología, Argentina, Grant PICT 99 No. 1-7160, by Ministerio de Educación de la Nación, Argentina, FOMEC 138, by the Fund for Medical Scientific Research (Belgium), and by the Belgian Directorate General for Higher Education and Scientific Research. 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.

^|| Member of Carrera del Investigador Científico, CONICET, Argentina. To whom correspondence should be addressed. Tel.: 54-341-4350661; Fax: 54-341-4390465; E-mail: toniuttaro{at}yahoo.com.ar.

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