title: Primary structure and phylogenetic relationships of a malate dehydrogenase gene from Giardia lamblia.
abstract: The lactate and malate dehydrogenases comprise a complex protein superfamily with multiple enzyme homologues found in eubacteria, archaebacteria, and eukaryotes. In this study we describe the sequence and phylogenetic relationships of a malate dehydrogenase (MDH) gene from the amitochondriate diplomonad protist, Giardia lamblia. Parsimony, distance, and maximum-likelihood analyses of the MDH protein family solidly position G. lamblia MDH within a eukaryote cytosolic MDH clade, to the exclusion of chloroplast, mitochondrial, and peroxisomal homologues. Furthermore, G. lamblia MDH is specifically related to a homologue from Trichomonas vaginalis. This MDH topology, together with published phylogenetic analyses of beta-tubulin, chaperonin 60, valyl-tRNA synthetase, and EF-1alpha, suggests a sister-group relationship between diplomonads and parabasalids. Since these amitochondriate lineages contain genes encoding proteins which are characteristic of mitochondria and alpha-proteobacteria, their shared ancestry suggests that mitochondrial properties were lost in the common ancestor of both groups.
authors.affiliation: Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, 7 MBL Street, Woods Hole, MA 02543-1015, USA.
authors.forename: A J
authors.initials: AJ
authors.lastname: Roger
authors.forename: H G
authors.initials: HG
authors.lastname: Morrison
authors.forename: M L
authors.initials: ML
authors.lastname: Sogin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003600:Cytosol / Q000201:enzymology; D016829:Giardia lamblia / Q000235:genetics*; D008291:Malate Dehydrogenase / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D015800:Protozoan Proteins / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014246:Trichomonas vaginalis / Q000235:genetics
chemical_list: D015800:Protozoan Proteins; D008291:Malate Dehydrogenase