Former Department of Molecular Genetics

Many activities of eukaryotic cells depend on a complex network of membrane-enclosed compartments. The biogenesis of membranes, the delivery of proteins to specific cellular compartments, protein secretion and endocytosis are mediated by vesicular intermediates. Transport vesicles bud from a donor compartment and, after docking to the correct target compartment, membrane fusion results in the delivery of cargo to the target organelle. Retrograde transport between compartments of the biosynthetic and the endocytic pathway assures a balance between loss and gain of membrane material and is a means to retrieve escaped resident proteins of individual organelles (Figure 1). The formation of transport vesicles, their correct targeting and the specificity of membrane fusion events require multicomponent transport machineries. Many of their components are highly conserved from the unicellular yeast to human brain cells.

In our research we focused on the following questions: What assures the accuracy of protein and membrane flow between different compartments in living cells? Which are the components of "protein machines" involved in vesicular transport, how do they interact and what functions do they fulfil? What, in particular, is the role of small GTPases in directing vesicular traffic at different stages of the exo- and endocytic pathways and how is their activity regulated?

Our research projects included:

1. ER-to-Golgi Transport

  • Role of the Sec1-related Sly1 protein which is essential for yeast cell viability and binds with high affinity to the t-SNARE Sed5p
  • Involvement of COPII components in fusion of ER-derived transport vesicles
  • Identification and biochemical analysis of Ypt1 GTPase-interacting proteins (membrane receptors, GTPase-activating and nucleotide exchange proteins)

2. Intra-Golgi Transport

  • Role of Ypt31/32 GTPases in Golgi transport (forward vs. retrograde transport)
  • Biochemical analysis of newly identified Ypt31/32-interacting Golgi proteins

3. Transport between Golgi and Endosomes

  • Functional studies of Ypt6p, a non-essential GTPase presumably involved in transport from endosomes to the Golgi
  • Biochemical analysis of proteins (designated Sys) which at high intracellular level suppress heat sensitivity and missorting of vacuolar proteins in cells lacking Ypt6p

4. Endocytosis

  • Endosome-to-vacuole transport components
  • Identification and biochemical analysis of factors regulating the activity of Ypt7p
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