PhD ceremony Ms. M.N. Krygowska: Peroxisome biogenesis and dynamics in Hansenula polymorpha

PhD ceremony: Ms. M.N. Krygowska

Dissertation: Peroxisome biogenesis and dynamics in Hansenula polymorpha

Promotor(s): prof. I.J. van der Klei

Faculty: Mathematics and Natural Sciences

Peroxisomes are important organelles to sustain life, also in man. They are very flexible with respect to their metabolic function and readily adapt their function in relation to metabolic needs. The thesis of Malgorzata Krygowska describes studies on the development and dynamics of peroxisomes in the methylotrophic yeast Hansenula polymorpha. Important breakthrough of her work is the groundbreaking discovery that the current models of de novo peroxisome formation and PMP sorting pathways are no longer generally valid and require adaptation.

In yeast, peroxisomes multiply by asymmetric fission. Krygowska observed that during fission a distinct set of peroxisomal membrane proteins (PMPs) is unevenly distributed over the mother and daughter peroxisomes. As a result the new, small organelles are formed that are fully equipped to rapidly grow and incorporate novel matrix proteins to perform their function in the new cell

Next, she studied the process of de novo peroxisome formation. Until now, Pex3 cells were assumed to lack peroxisomal structures and used the ER as membrane template for de novo peroxisome creation Unexpected, Krygowska observed vesicular structures in pex3 cells that developed into normal peroxisomes upon re-introduction of Pex3. This groundbreaking discovery implies that the current models on peroxisome de novo synthesis and PMP sorting are no longer valid and require adaptation

Additionally, Krygowska studied the involvement of the H. polymorpha Pex23 protein family (Pex23 and Pex32) in peroxisome biology. She discovered that Pex32 has a major impact on organelle biogenesis, whereas Pex23 most probably stimulates de novo peroxisome formation.

Finally, Krygowska identified a bona fide homologue of S. cerevisiae Inp2 in H. polymorpha, which plays a role in peroxisome distribution over mother and daughter cells during cell division.