Proteins of the glycine decarboxylase complex in the hydrogenosome of Trichomonas vaginalis.
Trichomonas vaginalis is a unicellular eukaryote that lacks mitochondria and contains a specialized organelle, the hydrogenosome, involved in carbohydrate metabolism and iron-sulfur cluster assembly. We report the identification of two glycine cleavage H proteins and a dihydrolipoamide dehydrogenase (L protein) of the glycine decarboxylase complex in T. vaginalis with predicted N-terminal hydrogenosomal presequences. Immunofluorescence analyses reveal that both H and L proteins are localized in hydrogenosomes, providing the first evidence for amino acid metabolism in this organelle. All three proteins were expressed in Escherichia coli and purified to homogeneity. The experimental Km of L protein for the two H proteins were 2.6 microM and 3.7 microM, consistent with both H proteins serving as substrates of L protein. Analyses using purified hydrogenosomes showed that endogenous H proteins exist as monomers and endogenous L protein as a homodimer in their native states. Phylogenetic analyses of L proteins revealed that the T. vaginalis homologue shares a common ancestry with dihydrolipoamide dehydrogenases from the firmicute bacteria, indicating its acquisition via a horizontal gene transfer event independent of the origins of mitochondria and hydrogenosomes.
Mukherjee
Mandira
M
Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, 609 Charles E. Young Drive East, Los Angeles, CA 90095-1489, USA.
Brown
Mark T
MT
McArthur
Andrew G
AG
Johnson
Patricia J
PJ
D000595:Amino Acid Sequence; D000818:Animals; D008058:Dihydrolipoamide Dehydrogenase / Q000235:genetics / Q000378:metabolism; D017125:Genes, Protozoan; D050959:Glycine Decarboxylase Complex / Q000235:genetics / Q000378:metabolism*; D050961:Glycine Decarboxylase Complex H-Protein / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D015388:Organelles / Q000201:enzymology; D010802:Phylogeny; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014246:Trichomonas vaginalis / Q000201:enzymology* / Q000235:genetics
D050961:Glycine Decarboxylase Complex H-Protein; D015800:Protozoan Proteins; D011994:Recombinant Proteins; D050959:Glycine Decarboxylase Complex; D008058:Dihydrolipoamide Dehydrogenase