Prolyl 4-hydroxylase : studies on collagen prolyl 4-hydroxylases and related enzymes using the green alga Chlamydomonas reinhardtii and two Caenorhabditis nematode species as model organisms
1University of Oulu, Faculty of Medicine, Department of Medical Biochemistry and Molecular Biology
2University of Oulu, Biocenter Oulu
3University of Oulu, Collagen Research Unit
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|Persistent link:|| http://urn.fi/urn:isbn:9789514284731
|Publish Date:|| 2007-05-15
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic dissertation to be presented, with the assent of the Faculty of Medicine of the University of Oulu, for public defence in the Auditorium of the Medipolis Research Center (Kiviharjuntie 11), on May 25th, 2007, at 10 a.m.
Associate Professor Simon Tuck
Professor Garry Wong
Collagen prolyl 4-hydroxylases (C-P4Hs) and related enzymes catalyze the hydroxylation of certain proline residues in animal collagens and plant hydroxyproline-rich proteins, respectively. Animal C-P4Hs and their isoenzymes have been characterized to date from humans, rodents, insects and nematodes. Most of the animal C-P4Hs are α2β2 tetramers in which protein disulphide isomerase (PDI) serves as the β subunit, but the nematode C-P4Hs characterized so far have unique molecular compositions. Two P4Hs have been cloned from the plant Arabidopsis thaliana and one from the Paramecium bursaria Chlorella virus-1, these being monomeric enzymes.
This thesis reports on the identification of a large P4H family in the green alga Chlamydomonas reinhardtii and the cloning and characterization of one member, Cr-P4H-1. This is a soluble monomer that hydroxylates in vitro several peptides representing sequences found in C. reinhardtii cell wall proteins. Lack of its activity led to a defective cell wall structure, indicating that Cr-P4H-1 is essential for proper cell wall assembly and that the other P4Hs cannot compensate for the lack of its activity.
Two C. elegans genes, Y43F8B.4 and C14E2.4, predicted to code for C-P4H α subunit-like polypeptides were analyzed. Three transcripts were generated from Y43F8B.4, one of them coding for a functional C-P4H α subunit named PHY-4.1. C14E2.4 turned out not to be a C-P4H α subunit gene, as a frame-shift led to the omission of codons for two catalytically critical residues. PHY-4.1 formed active tetramers and dimers with PDI-2 and had unique substrate requirements in that it hydroxylated certain other proline-rich sequences besides collagen-like peptides. Inactivation of the Y43F8B.4 gene led to no obvious morphological abnormalities. Spatial expression of the phy-4.1 transcript and PHY-4.1 polypeptide was localized to the pharynx and the excretory duct. Taken together, these data indicate that PHY-4.1 is not involved in the hydroxylation of cuticular collagens but is likely to have other substrates in vivo.
Cloning and characterization of the PHY-1 and PHY-2 subunits from the closely related nematode Caenorhabditis briggsae revealed distinct differences in assembly properties between the C. elegans and C. briggsae PHY-2 subunits in spite of their high amino acid sequence identity. Genetic disruption of C. briggsae phy-1 resulted in a less severe phenotype than that observed in C. elegans, evidently on account of its more efficient assembly of the C. briggsae PHY-2 to an active C-P4H explaining the milder phenotype. Rescue of C. elegans and C. briggsae phy-1 mutants was achieved by injection of a wild-type phy-1 gene from either species.
Acta Universitatis Ouluensis. D, Medica
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