Tetrahydrobiopterin is an essential cofactor for aromatic amino acid hydroxylases, ether lipid oxidase and nitric oxide synthases. Its biosynthesis in mammals is regulated by the activity of the homodecameric enzyme GCH (GTP cyclohydrolase I; EC 3.5.4.16). In previous work, catalytically inactive human GCH splice variants differing from the wild-type enzyme within the last 20 C-terminal amino acids were identified. In the present study, we searched for a possible role of these splice variants. Gel filtration profiles of purified recombinant proteins showed that variant GCHs form high-molecular-mass oligomers similar to the wild-type enzyme. Co-expression of splice variants together with wild-type GCH in mammalian cells revealed that GCH levels were reduced in the presence of splice variants. Commensurate with these findings, the GCH activity obtained for wild-type enzyme was reduced 2.5-fold through co-expression with GCH splice variants. Western blots of native gels suggest that splice variants form decamers despite C-terminal truncation. Therefore one possible explanation for the effect of GCH splice variants could be that inactive variants are incorporated into GCH heterodecamers, decreasing the enzyme stability and activity.
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Research Article|
October 27 2006
Interaction of human GTP cyclohydrolase I with its splice variants
Maya J. Pandya;
Maya J. Pandya
1
1Division of Biological Chemistry, Biocenter, Innsbruck Medical University, Fritz-Pregl-Strasse 3, A-6020 Innsbruck, Austria
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Georg Golderer;
Georg Golderer
1Division of Biological Chemistry, Biocenter, Innsbruck Medical University, Fritz-Pregl-Strasse 3, A-6020 Innsbruck, Austria
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Ernst R. Werner;
Ernst R. Werner
1Division of Biological Chemistry, Biocenter, Innsbruck Medical University, Fritz-Pregl-Strasse 3, A-6020 Innsbruck, Austria
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Gabriele Werner-Felmayer
Gabriele Werner-Felmayer
2
1Division of Biological Chemistry, Biocenter, Innsbruck Medical University, Fritz-Pregl-Strasse 3, A-6020 Innsbruck, Austria
2To whom correspondence should be addressed (email gabriele.werner-felmayer@i-med.ac.at).
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Publisher: Portland Press Ltd
Received:
May 23 2006
Revision Received:
July 13 2006
Accepted:
July 19 2006
Accepted Manuscript online:
July 19 2006
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London
2006
Biochem J (2006) 400 (1): 75–80.
Article history
Received:
May 23 2006
Revision Received:
July 13 2006
Accepted:
July 19 2006
Accepted Manuscript online:
July 19 2006
Citation
Maya J. Pandya, Georg Golderer, Ernst R. Werner, Gabriele Werner-Felmayer; Interaction of human GTP cyclohydrolase I with its splice variants. Biochem J 15 November 2006; 400 (1): 75–80. doi: https://doi.org/10.1042/BJ20060765
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