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Theses and Dissertations

An ancestral role in de novo peroxisome assembly is retained by the divisional peroxin Pex11 in the yeast Yarrowia lipolytica Open Access


Other title
Evolutionary cell biology
Cell biology
Type of item
Degree grantor
University of Alberta
Author or creator
Klute, Mary J.
Supervisor and department
Dacks, Joel (Cell Biology)
Rachubinski, Richard (Cell Biology)
Examining committee member and department
Simmonds, Andrew (Cell Biology)
Dacks, Joel (Cell Biology)
Kowalewska-Grochowska, Kinga (Medical Microbiology and Immunology)
Rachubinski, Richard (Cell Biology)
Department of Cell Biology

Date accepted
Graduation date
Master of Science
Degree level
This thesis is on peroxisome evolution and reports my findings with regard to two major aspects of this process. First, I investigated the evolution of a peroxisomal protein family for which large expansions had been noted in diverse eukaryotes from a comparative genomic perspective and combined these findings with functional data delving into the evolutionary history of this protein family. Second, I studied the peroxisomal protein complement of three newly available eukaryotic genomes. The peroxin (protein required for peroxisome biogenesis) Pex11p has a well recognized role in peroxisome division in diverse eukaryotes. Pex11p remodels and elongates the membranes of peroxisomes prior to the recruitment of dynamin-related GTPases that act in membrane scission to physically divide peroxisomes. I performed a comprehensive comparative genomics survey to understand the significance of the evolution of the Pex11 protein family in yeast and other eukaryotes. Pex11p itself is highly conserved and ancestral, and has undergone numerous lineage-specific duplications, while other Pex11 protein family members are fungal-specific innovations. Functional characterization of the in silico predicted Pex11 protein family members of the yeast Yarrowia lipolytica, i.e. Pex11p, Pex11Cp and Pex11/25p, demonstrated that Pex11Cp and Pex11/25p function in the regulation of peroxisome size and number characteristic of Pex11 protein family members. Unexpectedly, deletion of PEX11 in Y. lipolytica produces cells that lack morphologically identifiable peroxisomes, mislocalize peroxisomal matrix proteins, and show preferential degradation of peroxisomal membrane proteins, i.e. they exhibit the classical pex mutant phenotype, which has not been reported for any other eukaryotic cell deleted for the PEX11 gene. My results demonstrate an unprecedented role for Pex11p in de novo peroxisome assembly. I also studied the peroxisomal protein complement of three medically and/or evolutionarily relevant eukaryotic genomes: the intestinal parasite Blastocystis hominis, Bodo saltans, a close relative of the parasitic trypanosomatids which contains a divergent peroxisome known as the glycosome, and Naegleria fowleri, better known as the ‘brain-eating amoeba’. I showed that Blastocystis lacks peroxisomal proteins, consistent with parasites generally lacking the peroxisome organelle. I demonstrated that B. saltans and N. fowleri encode a relatively complete PEX gene complement, with certain losses. I wrote a program, PTS Finder, to predict proteins targeted to the peroxisome, and used it during these analyses.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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