title: Evidence for an early evolutionary emergence of gamma-type carbonic anhydrases as components of mitochondrial respiratory complex I.
abstract: BACKGROUND
  The complexity of mitochondrial complex I (CI; NADH:ubiquinone oxidoreductase) has increased considerably relative to the homologous complex in bacteria. Comparative analyses of CI composition in animals, fungi and land plants/green algae suggest that novel components of mitochondrial CI include a set of 18 proteins common to all eukaryotes and a variable number of lineage-specific subunits. In plants and green algae, several purportedly plant-specific proteins homologous to gamma-type carbonic anhydrases (gammaCA) have been identified as components of CI. However, relatively little is known about CI composition in the unicellular protists, the characterizations of which are essential to our understanding of CI evolution.
  
  
  RESULTS
  We have performed a tandem mass spectrometric characterization of CI from the amoeboid protozoon Acanthamoeba castellanii. Among the proteins identified were two gammaCA homologs, AcCa1 and AcCa2, demonstrating that gammaCA proteins are not specific to plants/green algae. In fact, through bioinformatics searches we detected gammaCA homologs in diverse protist lineages, and several of these homologs are predicted to possess N-terminal mitochondrial targeting peptides.
  
  
  CONCLUSIONS
  The detection of gammaCAs in CI of Acanthamoeba, considered to be a closer relative of animals and fungi than plants, suggests that gammaCA proteins may have been an ancestral feature of mitochondrial CI, rather than a novel, plant-specific addition. This assertion is supported by the presence of genes encoding gammaCAs in the nuclear genomes of a wide variety of eukaryotes. Together, these findings emphasize the importance of a phylogenetically broad characterization of CI for elucidating CI evolution in eukaryotes.
authors.affiliation: Centre for Comparative Genomics and Evolutionary Bioinformatics, Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 1X5, Canada.
authors.forename: Ryan M R
authors.initials: RM
authors.lastname: Gawryluk
authors.forename: Michael W
authors.initials: MW
authors.lastname: Gray
mesh_terms: D048248:Acanthamoeba castellanii / Q000201:enzymology / Q000235:genetics*; D000595:Amino Acid Sequence; D002256:Carbonic Anhydrases / Q000235:genetics*; D019295:Computational Biology; D019143:Evolution, Molecular; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D010802:Phylogeny; D015800:Protozoan Proteins / Q000235:genetics / Q000302:isolation & purification; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid
chemical_list: D024101:Mitochondrial Proteins; D015800:Protozoan Proteins; D002256:Carbonic Anhydrases