Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.12.7.2 (hydrogenase)
 3,522 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Most modern eukaryotes diverged from a common ancestor that contained the alpha-proteobacterial endosymbiont that gave rise to mitochondria. The 'amitochondriate' anaerobic protist parasites that have been studied to date, such as Giardia and Trichomonas harbor mitochondrion-related organelles, such as mitosomes or hydrogenosomes. Yet there is one remaining group of mitochondrion-lacking flagellates known as the Preaxostyla that could represent a primitive 'pre-mitochondrial' lineage of eukaryotes. To test this hypothesis, we conducted an expressed sequence tag (EST) survey on the preaxostylid flagellate Trimastix pyriformis, a poorly-studied free-living anaerobe. Among the ESTs we detected 19 proteins that, in other eukaryotes, typically function in mitochondria, hydrogenosomes or mitosomes, 12 of which are found exclusively within these organelles. Interestingly, one of the proteins, aconitase, functions in the tricarboxylic acid cycle typical of aerobic mitochondria, whereas others, such as pyruvate:ferredoxin oxidoreductase and [FeFe] hydrogenase, are characteristic of anaerobic hydrogenosomes. Since Trimastix retains genetic evidence of a mitochondriate ancestry, we can now say definitively that all known living eukaryote lineages descend from a common ancestor that had mitochondria.
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PMID:Genetic evidence for a mitochondriate ancestry in the 'amitochondriate' flagellate Trimastix pyriformis. 1816 42

Protists that live under low-oxygen conditions often lack conventional mitochondria and instead possess mitochondrion-related organelles (MROs) with distinct biochemical functions. Studies of mostly parasitic organisms have suggested that these organelles could be classified into two general types: hydrogenosomes and mitosomes. Hydrogenosomes, found in parabasalids, anaerobic chytrid fungi, and ciliates, metabolize pyruvate anaerobically to generate ATP, acetate, CO(2), and hydrogen gas, employing enzymes not typically associated with mitochondria. Mitosomes that have been studied have no apparent role in energy metabolism. Recent investigations of free-living anaerobic protists have revealed a diversity of MROs with a wider array of metabolic properties that defy a simple functional classification. Here we describe an expressed sequence tag (EST) survey and ultrastructural investigation of the anaerobic heteroloboseid amoeba Sawyeria marylandensis aimed at understanding the properties of its MROs. This organism expresses typical anaerobic energy metabolic enzymes, such as pyruvate:ferredoxin oxidoreductase, [FeFe]-hydrogenase, and associated hydrogenase maturases with apparent organelle-targeting peptides, indicating that its MRO likely functions as a hydrogenosome. We also identified 38 genes encoding canonical mitochondrial proteins in S. marylandensis, many of which possess putative targeting peptides and are phylogenetically related to putative mitochondrial proteins of its heteroloboseid relative Naegleria gruberi. Several of these proteins, such as a branched-chain alpha keto acid dehydrogenase, likely function in pathways that have not been previously associated with the well-studied hydrogenosomes of parabasalids. Finally, morphological reconstructions based on transmission electron microscopy indicate that the S. marylandensis MROs form novel cup-like structures within the cells. Overall, these data suggest that Sawyeria marylandensis possesses a hydrogenosome of mitochondrial origin with a novel combination of biochemical and structural properties.
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PMID:Sawyeria marylandensis (Heterolobosea) has a hydrogenosome with novel metabolic properties. 2103 80