 |
Background Research Publications Current Lab |
| Dr Thimo Kurz |
| E: t.kurz@dundee.ac.uk |
| T: 44 1382 388371 |
| F: 44 1382 388500 |
Dr Thimo Kurz
Research
Function and Control of Ubiquitin and Ubiquitin-like Protein Conjugation Systems
Many cellular processes are regulated by post-translational protein modifications with ubiquitin (UB) or ubiquitin-like (UBL) molecules. For example, degradation through the Ubiquitin-Proteasome System (UPS) accounts for a major part of targeted protein destruction in a cell. During this process, three enzymes called E1 activating enzyme, E2 conjugating enzyme, and E3 ubiquitin ligase attach a ubiquitin chain to a substrate protein, which as a consequence is recognized and destroyed by the protease 26S-proteasome.
Ubiquitin-like molecules are attached to substrate proteins using distinct E1, E2, and E3 enzymes. Unlike ubiquitin, UBLs don’t target their substrates for degradation, but rather change their activity by, for example, providing a new binding surface for interaction partners.
Defects in ubiquitin and ubiquitin-like protein conjugation systems have been implicated in a variety of human diseases, including cancer and neurodegeneration. The development of these diseases is often associated with a malfunction of E3 ligases, the enzymes that attach the UB or UBL moiety to the substrate.
My laboratory is interested in elucidating the molecular mechanisms underlying E3 Ligase activity. We use the budding yeast S. cerevisiae and mammalian tissue culture cells as model systems to answer the outstanding questions in the field. Our research aims at understanding the basic biological functions of E3 ligases, but also is directed at elucidating the molecular defects associated with the development of human diseases.
Cullin-based E3 Ubiquitin Ligases
One focus of the laboratory is the regulation of cullin-based E3 ubiquitin ligases. Cullin proteins are scaffolds for a subgroup of multi-subunit E3 ubiquitin ligases, the best characterized of which is the yeast SCF complex (Fig. 1).
(Figure 1)
In humans, the SCF E3 ubiquitin ligase degrades the tumour suppressor and cyclin-dependent-kinase inhibitor p27 at the G1/S transition of the cell cycle. Consequently, high levels of SCFSKP2 activity correlates with low p27 levels in many human tumours. In addition to cell cycle regulation, cullin ligases also play a role in many other cellular processes, including mitosis, development, and various signaling pathways.
The ubiquitin-like protein Nedd8
Cullin-based E3 ubiquitin ligases are regulated by the ubiquitin-like protein Nedd8. Nedd8 is attached covalently to a specific lysine residue on the C-terminus of the cullin (neddylation; Fig.2), which activates the E3 by removing the ligase assembly inhibitor Cand1 and by inducing structural changes in the cullin C-terminus.
(Figure 2)
We recently identified Dcn1 (defective-for-cullin-neddylation-1), a previously uncharacterized, but evolutionarily highly conserved yeast protein required for cullin neddylation. Using biochemical and genetic techniques, we could demonstrate that Dcn1 is a cullin-directed Nedd8 E3 ligase. Dcn1 binds directly to cullins and the Nedd8 E2 enzyme, and facilitates neddylation by acting as a scaffold for the reaction.
In collaboration with the Sicheri group at the Samuel Lunenfeld Research Institute in Toronto, Canada, we solved the crystal structure of Dcn1 by X-ray crystallography. This work revealed that the protein consists of an N-terminal UBA-like ubiquitin-binding domain, and a C-terminal domain of novel architecture, called PONY (potentiating neddylation) domain (Fig. 3).
(Figure 3)
The human genome encodes five Dcn1 homologues, all of which contain a C-terminal PONY domain, but differ in the structure of their N-termini. The closest human homologue, Dcnl1 has been reported to act as an oncogene and is amplified in squamous cell carcinomas. Further studies of Dcn1 and Dcnl1 may thus help us understand how Dcnl1 amplification results in cancer formation.
The role of the other four human homologues remains elusive. However, given the conservation of the PONY domain, it is likely that they also function in protein neddylation. In the future it will be important to determine whether these proteins indeed act as Nedd8 E3 ligases and, if so, to identify their neddylation substrates.
References
- Kurz, T.,* Chou, Y.C.,* Willems, A.R., Meyer-Schaller, N., Hecht, M-L., Tyers, M., Peter, M. and Sicheri, F. (2008). Dcn1 functions as scaffold-type E3 ligase for cullin neddylation. Mol Cell. 29, pp. 23-35.
- Luke, B., Versini, G., Jaquenod, M., Zaidi, I.W., Kurz, T., Pintard, L., Pasero, P. and Peter, M. (2006). The S.cerevisiae cullin Rtt101p regulates the stability of replication forks at damaged DNA and natural pause sites. Curr Biol. 16, pp. 786-792.
- Bowerman, B. and Kurz, T. (2006). Degrade to create: ubiquitin-mediated proteolysis and early embryogenesis in C. elegans. Development. 133, pp. 773-784. Review.
- Kurz, T., Özlü, N., Rudolf, F., O’Rourke, S.M., Luke, B., Hofmann, K., Hyman, A.A., Bowerman, B. and Peter, M. (2005). The Conserved Protein DCN-1/Dcn1p is Required for Cullin Neddylation in C. elegans and S. cerevisiae. Nature. 435, pp. 1257-1261.
- Pintard, L., Willis, J.H., Willems, A., Johnson, J.L., Srayko, M., Kurz, T., Glaser, S., Mains, P.E., Tyers, M., Bowerman, B. and Peter, M. (2003). The BTB protein MEL-26 is a substrate-specific adaptor of the CUL-3 ubiquitin-ligase. Nature. 425, pp. 311-316.
- Kurz, T.,* Pintard, L.,* Glaser, S., Willis, J.H., Peter, M. and Bowerman, B. (2003). Neddylation and Deneddylation of CUL-3 Is Required to Target MEI-1/Katanin for Degradation at the Meiosis-to-Mitosis Transition in C. elegans. Curr Biol. 13, pp. 911-921.
- Kurz, T., Pintard, L., Willis, J.H., Hamill, D.R., Gonczy, P., Peter, M. and Bowerman, B. (2002). Cytoskeletal regulation by the Nedd8 ubiquitin-like protein modification pathway. Science. 295, pp. 1294-1298.
University of Dundee