Structural biology of ubiquitin-dependent protein degradation

The lab has open positions for Postdocs, PhD students and Diploma / Masters students. Talented and motivated people preferably with a background in structural biology, NMR spectroscopy and / or biochemistry are welcome to apply. To apply, please send an email including a cover letter and a CV to: silke.wiesner[at]tuebingen.mpg.de. Students applying for a PhD position should hold a Diploma or Masters degree in Biochemistry or Chemistry.

Research Interests

Protein Ubiquitination

The attachment of the small protein Ubiquitin is one of the most abundant post-translational modifications in eukaryotes and plays a role in virtually all signal transduction pathways. Ubiquitination marks proteins for degradation to control the abundance of key regulators in the cell and thus plays a role e.g. in cell cycle transition and the establishment of protein gradients in polarized cells and developmental processes. Aberrant ubiquitination enzyme function gives rise to cellular dysfunctions that cause numerous human diseases. Although the basic principles of Ub protein modification have been identified, the exact catalytic mechanism of the ubiquitination reaction is still unclear.

The ubiquitination reaction involves in general the sequential action of an activating (E1), a conjugating (E2), and a ligating (E3) enzyme. Apart from certain classes of E3s, ubiquitination enzymes contain a catalytic cysteine residue that forms a thioester intermediate with the carboxyl terminus of Ub, before the latter is covalently attached to a substrate lysine residue via an isopeptide bond (Figure 1).

Figure 1. Left panel: Schematic representation of the Ubiquitination reaction involving a HECT-type E3. Question marks highlight the unknown mechanisms underlying Ub transfer and isopeptide bond formation. Right panel: 3D protein structure of a HECT domain (E3 ligase) - UbcH7 (E2 enzyme) complex

Current research projects aim at identifying and characterizing binding surfaces and conformational changes in HECT-type ubiquitin ligases at different steps of the ubiquitination reaction using biomolecular NMR spectroscopy in combination with biochemical methods.

Cell polarity

Polarity is a fundamental property of all cells and refers to the asymmetry in function, shape or content of a cell created through unequal distribution of its molecular components. Cell polarity is critical for various cellular processes ranging from cell migration to asymmetric cell division (Figure 2) and is indispensable for the development of multicellular organisms. Loss of cell polarity is highly correlated with cancer pathogenesis. Despite its diverse cellular and developmental functions, the molecular machinery mediating cell polarity is evolutionary conserved in eukaryotes and involves a core network of modular protein interactions that are restricted to specific subcellular locations (Figure 2). We are studying how conformational changes and intra- and intermolecular interactions regulate the activity and subcellular localization of polarity proteins and thereby control the establishment and maintenance of cell polarity.

Figure 2. Localization of Par-3/Par-6/aPKC complexes in polarized cells. The asymmetric distribution of cell fate determinants enables cell differentiation (upper left panel), while the spatial and temporal restriction of morphogen- and cytokine-receptor interactions directs cell migration during embryonic development and immune surveillance (upper right panel). Furthermore, spatially and functionally restricted subcompartments underlie the function of neurons (lower left panel) and epithelial cells (lower right panel).

Current research projects aim at characterizing interactions among polarity proteins and between polarity proteins and HECT-type Ubiquitin ligases to provide a structural basis for polarity protein localization and to understand the molecular mechanisms underlying the establishment and maintenance of cell polarity.

NMR and X-ray equipment

The group has access to a 600 MHz and an 800 MHz NMR spectrometer, both installed at the institute in 2008. Furthermore, we have access to an in-house X-ray source, a honeybee crystallization robot and measurement time at the Swiss Light Source synchrotron in Villingen, Switzerland.

Teaching Material

Structural Biology Module (Biochemistry, University of Tübingen)

• Lecture: NMR Applications
• Script for the practical: NMR Practical

Selected Publications

Wiesner S, Ogunjimi AA, Wang H-R, Rotin D, Sicheri F, Wrana JL, Forman-Kay JD. (2007) Auto-inhibition of the HECT-type Ubiquitin protein ligase Smurf2 through its C2 domain. Cell 130:651-62.

Wiesner S*, Wybenga-Groot LE*, Warner N, Lin H, Pawson T, Forman-Kay JD, Sicheri F. (2006) A change in conformational dynamics underlies the activation of Eph receptor tyrosine kinases. EMBO J. 25: 4686-96.

Hantschel O*, Wiesner S*, Güttler T, Mackereth CD, Rix LL, Mikes Z, Dehne J, Görlich D, Sattler M, Superti-Furga G (2005) Structural basis for the cytoskeletal association of Bcr-Abl/c-Abl. Mol. Cell 19: 461-73.

*Equal contribution

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