Dr Ewald Hettema
Reader in Molecular Cell Biology
Tel: 0114 222 2732
My group aims to improve understanding of the molecular mechanisms underlying peroxisome dynamics at the cellular level.
Cells contain a large number of distinct membrane bound organelles. These compartments rely on complex machineries to acquire and maintain their unique composition and function. We are studying one of these organelles, the peroxisome. Lack of functional peroxisomes results in a deficiency of a large number of enzymatic reactions and a disorder called Zellweger (ZS-) or cerebro-hepato-renal syndrome. Proteins required for peroxisome formation are called peroxins and these have been found mutated in ZS patients.
Peroxisomes multiply by growth and division.
The endoplasmic reticulum (ER) provides peroxisomes with membrane constituents allowing these organelles to grow, after which the organelles divide and distribute between mother and daughter cell. The number of peroxisomes per cell is influenced by intracellular and extracellular factors and these can induce proliferation or breakdown. How these processes are regulated and integrated into cellular metabolism is poorly understood.
Fig 2A. Peroxisomes multiply and are subsequently transported to the newly forming daughter cell via an actin-myosin-based process. Approximately half the number of the peroxisomes are anchored to the periphery of mother cells and remain there. These opposing processes ensure peroxisome segregation with high fidelity. Fig 2B. Peroxisomes can be induced to proliferate under conditions of high requirement for these organelles. A subsequent shift to conditions where peroxisomes are superfluous induces their rapid breakdown by autophagy. Selective breakdown of peroxisomes is named pexophagy.
Genetic model organisms to study peroxisome dynamics and functioning
We and others have been using Saccharomyces cerevisiae as our model system and mutants have been identified that are disturbed in various aspects of peroxisome dynamics. These mutants have been instrumental in unravelling the underlying mechanisms of peroxisome formation, multiplication and segregation. We have recently focussed on the peroxisomal membrane protein Pex3. Lack of Pex3 results in a complete absence of peroxisomal structures. We have now found that Pex3 is also involved in peroxisome segregation during cell division and peroxisome turnover. It does this by binding of process-specific factors and therefore may act as a scaffold for the regulation of peroxisome dynamics.
Fig 3 shows. Mutants in S.cerevisiae cells are gene deletion mutants. Mutant phenotypes in D. melanogaster S2 cells were created by temporary inactivation of genes with RNAi. Blue circumference of yeast cells is artificially coloured bright field image. Nuclei are stained with DAPI in S2 cells and artificially coloured blue in images.
More recently we have extended our studies into other model organisms including the fruit fly Drosophila melanogaster, the slime mould Dictyostelium discoideum and human cells. For instance, a genome-wide RNAi screen in Drosophila cells identified many of the known proteins involved in peroxisome formation and peroxisome multiplication. Interestingly, we also identified several new genes that appear to be involved in formation and regulation of peroxisome dynamics. We use molecular cell biological approaches including live-cell imaging, genome-wide RNAi screens, yeast genetics, proteomics and protein-protein interaction studies to characterise the function of these new proteins.
Although our main interest is in a fundamental understanding of peroxisome dynamics and its role in peroxisome functioning, we are also following up on lines of research that potentially have medical implications.
Eukaryotic cell biology, yeast genetics, Saccharomyces cerevisiae, peroxisomes, autophagy, peroxisome biogenesis disorders
I welcome applications from self-funded prospective home and international PhD students; see examples of possible projects below. You can apply for a PhD position in MBB here.
Contact me at firstname.lastname@example.org for further information.
Examples of self-funded PhD projects:
Development of genome editing tools for use in non-model organisms with biotechnological potential
Construction of synthetic organelles for biotechnology
Investigations into the molecular mechanisms of organelle movement and inheritance
Characterisation of peroxisome fission and formation
Fungal extracellular vesicle formation
Level 3 Modules
MBB342 Genetics of Cell Growth and Division
Level 1 Modules
MBB164 Molecular Biology
- Two NAD-linked redox shuttles maintain the peroxisomal redox balance in Saccharomyces cerevisiae. Scientific Reports, 7(1). View this article in WRRO
- Pnc1 piggy-back import into peroxisomes relies on Gpd1 homodimerisation.. Sci Rep, 7, 42579-42579. View this article in WRRO
- Cell biology: Organelle formation from scratch. Nature, 542, 174-175.
- Reevaluation of the role of Pex1 and dynamin-related proteins in peroxisome membrane biogenesis. The Journal of Cell Biology, 211(5), 1041-1056. View this article in WRRO
- Multiple Pathways for Protein Transport to Peroxisomes. Journal of Molecular Biology, 427(6), 1176-1190. View this article in WRRO
- Evolving models for peroxisome biogenesis. Current Opinion in Cell Biology, 29(1), 25-30. View this article in WRRO
- Deficiency of the exportomer components Pex1, Pex6, and Pex15 causes enhanced pexophagy in Saccharomyces cerevisiae.. Autophagy, 10(5), 835-845. View this article in WRRO
- Intra-ER sorting of the peroxisomal membrane protein Pex3 relies on its luminal domain.. Biol Open, 2(8), 829-837. View this article in WRRO
- Pexophagy is activated in a subset of peroxisome assembly mutants. MOLECULAR BIOLOGY OF THE CELL, 24.
- Farnesyl diphosphate synthase, the target for nitrogen-containing bisphosphonate drugs, is a peroxisomal enzyme in the model system Dictyostelium discoideum.. Biochem J, 447(3), 353-361. View this article in WRRO
- Atg36: the Saccharomyces cerevisiae receptor for pexophagy.. Autophagy, 8(11), 1680-1681.
- Pex3-anchored Atg36 tags peroxisomes for degradation in Saccharomyces cerevisiae.. EMBO J, 31(13), 2852-2868. View this article in WRRO
- Peroxisome biogenesis: Recent advances. Current Opinion in Cell Biology, 23(4), 421-426.
- A role for the dynamin-like protein Vps1 during endocytosis in yeast.. J Cell Sci, 123(Pt 20), 3496-3506.
- A dual function for Pex3p in peroxisome formation and inheritance.. J Cell Biol, 187(4), 463-471. View this article in WRRO
- How peroxisomes multiply.. J Cell Sci, 122(Pt 14), 2331-2336.
- Dnm1p-dependent peroxisome fission requires Caf4p, Mdv1p and Fis1p.. J Cell Sci, 121(Pt 10), 1633-1640.
- Yeast peroxisomes multiply by growth and division.. J Cell Biol, 178(3), 399-410. View this article in WRRO
- Immunological methods. METHOD MICROBIOL, 36, 241-268.
- Bsd2 binds the ubiquitin ligase Rsp5 and mediates the ubiquitination of transmembrane proteins.. EMBO J, 23(6), 1279-1288.
- Retromer and the sorting nexins Snx4/41/42 mediate distinct retrieval pathways from yeast endosomes.. EMBO J, 22(3), 548-557.
- A role for Vps1p, actin, and the Myo2p motor in peroxisome abundance and inheritance in Saccharomyces cerevisiae.. J Cell Biol, 155(6), 979-990. View this article in WRRO
- Identification of a peroxisomal ATP carrier required for medium-chain fatty acid beta-oxidation and normal peroxisome proliferation in Saccharomyces cerevisiae.. Mol Cell Biol, 21(13), 4321-4329.
- Peroxisomal beta-oxidation in yeast: new insights into the mechanisms involved with emphasis on the role of PEX11P and YPR128CP, two peroxisomal membrane proteins, in betaoxidation and peroxisomal proliferation. Biochemical Society Transactions, 29(1), A29-A29.
- Pex11p plays a primary role in medium-chain fatty acid oxidation, a process that affects peroxisome number and size in Saccharomyces cerevisiae.. J Cell Biol, 150(3), 489-498. View this article in WRRO
- Caenorhabditis elegans has a single pathway to target matrix proteins to peroxisomes.. EMBO Rep, 1(1), 40-46.
- Transport of fatty acids and metabolites across the peroxisomal membrane.. Biochim Biophys Acta, 1486(1), 18-27.
- Nuclear receptors arose from pre-existing protein modules during evolution.. Trends Biochem Sci, 25(5), 227-228.
- Saccharomyces cerevisiae pex3p and pex19p are required for proper localization and stability of peroxisomal membrane proteins.. EMBO J, 19(2), 223-233.
- In silicio search for genes encoding peroxisomal proteins in Saccharomyces cerevisiae.. Cell Biochem Biophys, 32 Spring, 1-8.
- Molecular characterization of carnitine-dependent transport of acetyl-CoA from peroxisomes to mitochondria in Saccharomyces cerevisiae and identification of a plasma membrane carnitine transporter, Agp2p.. EMBO J, 18(21), 5843-5852.
- Import of proteins into peroxisomes.. Biochim Biophys Acta, 1451(1), 17-34.
- Enlargement of the endoplasmic reticulum membrane in Saccharomyces cerevisiae is not necessarily linked to the unfolded protein response via Ire1p.. FEBS Lett, 453(1-2), 210-214.
- The cytosolic DnaJ-like protein djp1p is involved specifically in peroxisomal protein import.. J Cell Biol, 142(2), 421-434. View this article in WRRO
- Molecular basis of rhizomelic chondrodysplasia punctata type I: high frequency of the Leu-292 stop mutation in 38 patients.. J Inherit Metab Dis, 21(3), 306-308.
- Acyl-CoA:dihydroxyacetonephosphate acyltransferase: cloning of the human cDNA and resolution of the molecular basis in rhizomelic chondrodysplasia punctata type 2.. Hum Mol Genet, 7(5), 847-853.
- Peroxisomal beta-oxidation of polyunsaturated fatty acids in Saccharomyces cerevisiae: isocitrate dehydrogenase provides NADPH for reduction of double bonds at even positions.. EMBO J, 17(3), 677-687.
- Transport of activated fatty acids by the peroxisomal ATP-binding-cassette transporter Pxa2 in a semi-intact yeast cell system.. Eur J Biochem, 249(3), 657-661.
- Rhizomelic chondrodysplasia punctata is a peroxisomal protein targeting disease caused by a non-functional PTS2 receptor.. Nat Genet, 15(4), 377-380.
- The ABC transporter proteins Pat1 and Pat2 are required for import of long-chain fatty acids into peroxisomes of Saccharomyces cerevisiae.. EMBO J, 15(15), 3813-3822.
- Transport of proteins and metabolites across the impermeable membrane of peroxisomes.. Cold Spring Harb Symp Quant Biol, 60, 649-655.
- The P-glycoprotein-related gene family in Leishmania.. Mol Biochem Parasitol, 68(1), 81-91.
- Differential protein import deficiencies in human peroxisome assembly disorders.. J Cell Biol, 125(4), 755-767. View this article in WRRO
- Variation in gene copy number and polymorphism of the human salivary amylase isoenzyme system in Caucasians.. Hum Genet, 89(2), 213-222.
- Direct and inverted DNA repeats associated with P-glycoprotein gene amplification in drug resistant Leishmania.. EMBO J, 10(4), 1009-1016.
- Electrophoretic characterization of posttranslational modifications of human parotid salivary alpha-amylase.. Electrophoresis, 12(1), 74-79.