PhD ceremony: B. de Vries, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen
Thesis: The biology of peroxisomes in Hansenula polymorpha
Promotor(s): prof. M. Veenhuis, prof. I.J. van der Klei
Faculty: Mathematics and Natural Sciences
Bart de Vries studied a peroxisomal membrane proteins, Pex14p. This protein is of importance for both the creation (biogenesis) as well as degradation (macropexophagy) of the peroxisome. We make a distinction between two types of peroxisomes in Hansenula polymorpha, ie. Mature organelles, which are in essence just “protein bags” wherein the enzymatic reactions take place and the young peroxisomes that actively import peroxisomal matrix proteins to grow.
Minute amounts of Pex14p suffice for macropexophagy, while this is insufficient for correct biogenesis. Pex14p may act as a switch at the moment macropexophagy is induced, this can explain why this minute amount of Pex14p is sufficient.
Furthermore we analyzed the roll of the first (conserved in all organisms) stretch of amino acids in Pex14p and their importance for the import of two classes of peroxisomal matrix proteins. We show here that two residues are essential for both types of matrix proteins as well as the shape of the protein in this stretch of amino acids.
We also studied the roll of a cytosolic SNARE protein in both biogenesis of peroxisomes and macropexophagy. In the absence of this protein, misshapen peroxisomes are formed, yet this does not affect the capability of the cells to grow like wild type op methanol. The cell is however, not capable of degrading these aberrant peroxisomes.
Finally, an in silico study of the genoom of H. polymorpha and Pichia pastoris resulted in 34 possible new putative peroxisomal proteins. An acetylspermidine oxidase with a deviant signal sequence was tested as a “proof-of-principle” for its localization and was found solely in the peroxisome.
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