Characterization of 3-hydroxyacyl-ACP dehydratase of mitochondrial fatty acid synthesis in yeast, humans and trypanosomes
1University of Oulu, Faculty of Science, Department of Biochemistry
2University of Oulu, Biocenter Oulu
|Online Access:||PDF Full Text (PDF, 0.7 MB)|
|Persistent link:|| http://urn.fi/urn:isbn:9789514286711
|Publish Date:|| 2007-12-05
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic dissertation to be presented, with the assent of the Faculty of Science of the University of Oulu, for public defence in Raahensali (Auditorium L10), Linnanmaa, on December 14th, 2007, at 12 noon
Docent Sirkka Keränen
Professor Wolfgang Schliebs
In eukaryotic cells, fatty acids are mainly synthesized in the cytoplasm, but recently, in yeast and in humans, the ability to synthesize fatty acids has been characterized in mitochondria. This mitochondrial pathway is similar to bacterial type II fatty acid synthesis (FAS). The main feature of mitochondrial FAS in yeast is the respiratory deficient phenotype and loss of cytochromes when any of genes encoding enzymes for mitochondrial FAS is deleted. Mitochondrial FAS has been demonstrated to have an important role in lipoic acid production, namely it synthesizes octanoyl-ACP, which is used as a precursor for lipoic acid. However, the role and function of mitochondrial FAS is not yet fully understood. Many components of the mitochondrial FAS pathway in yeast have been identified according to their similarity to bacterial counterparts, but 3-hydroxyacyl-ACP dehydratase does not show any easily recognizable similarity to bacterial dehydratases and thus remained unidentified.
In this study 3-hydroxyacyl-ACP dehydratases of mitochondrial FAS were characterized from the yeast Saccharomyces cerevisiae, humans, and the human pathogen Trypanosoma brucei. The yeast 3-hydroxyacyl-ACP dehydratase (Htd2p) was identified by using a genetic screen, and this protein was shown to be encoded by open reading frame (ORF) YHR067w. The product of this gene shows mitochondrial localization and exhibits hydratase 2 activity. The deletion of HTD2 leads to a respiratory deficient phenotype, loss of cytochromes, reduced lipoic acids levels and changes in mitochondrial morphology.
The ORF encoding human 3-hydroxyacyl-ACP hydratase (HsHTD2) was identified by functional complementation of the respiratory deficient phenotype of the yeast htd2 mutant with a human cDNA library. The complementing cDNA was previously identified as the RPP14 transcript encoding the 14 kDa subunit of the human RNase P complex. It was found that this transcript contains another 3' ORF, which encodes a protein that displays hydratase 2 activity and has mitochondrial localization. The bicistronic nature of the transcript is conserved in vertebrates and indicates a genetic link between mitochondrial FAS and RNA processing. The mitochondrial 3-hydroxyacyl-ACP hydratase in T. brucei is homologous to human HTD2, can complement the yeast respiratory deficient phenotype, exhibits hydratase 2 activity and localizes to the T. brucei mitochondrion.
Acta Universitatis Ouluensis. A, Scientiae rerum naturalium
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