Figure 1: (A) Solid phase synthesis of phosphoinositides for the preparation of libraries for SAR studies with lipid phosphatases (Bru et al., Chem. Sci. 2012). (B) Selective activators of PP1 in cells enable us to gain new insights into PP1 biology (Angew. Chem. Int. Ed. 2012, Chem. Biol. 2013)
Figure 2: DEPOD, the human dephosphorylation database (Li et al., Sci. Signal. 2013; Duan et al., Nucleic Acids Res. 2015)
The Köhn group combines molecular biology, biochemistry and synthetic chemistry to develop new approaches to study phosphatases, which can play a major role in cancer.
Previous and current research
Within intracellular signalling networks, phosphatases are counter players of kinases and play crucial roles in health and disease. Despite their importance, knowledge about their function, regulation and substrate interaction is still limited, and their investigation is challenging also because of the lack of tools to selectively target them. We aim to fill that void using interdisciplinary approaches.
We study the molecular mechanisms of the cancer-promoting PRL (phosphatase of regenerating liver) phosphatases using biochemical and molecular cell biology approaches, and we develop specific inhibitors for them. We observed phosphoinositidephosphatase activity for PRL-3 (McParland et al., Biochemistry 2011), prompting us to use phosphoinositides for substratebased inhibitor design. Therefore, we developed a solid-phase synthesis strategy (Bru et al., Chem. Sci. 2012; figure 1) enabling the parallel synthesis of phosphoinositide analogues. Moreover, through a combined in silico and biochemical approach, we discovered a cell-active inhibitor for the PRLs (Hoeger et al., Eur. J. Med. Chem. 2014).
Protein phosphatase-1 (PP1) is the ubiquitous phosphatase responsible for a majority of all dephosphorylation reactions on Ser/Thr residues inside cells. We developed the first and only selective chemical PP1-modulator, which activates it inside cells (Chatterjee et al., Angew. Chem. Int. Ed. 2012; figure 1). We are extending the PP1 toolkit, and will apply it to study PP1.
We created and maintain the human DEPhOsphorylation Database: DEPOD (figure 2), and have used it to re-classify the human phosphatome and to analyse phosphatase substrate specificities and their relation to kinases (Li et al., Sci. Signal. 2013; Duan et al., Nucleic Acids Res. 2015).
In the area of chemical tool development, we have established a strategy to design protein tyrosine phosphatase (PTP) inhibitors that can also function as detection tools (Meyer et al., ACS Chem. Biol. 2014). Moreover, using unnatural amino acid mutagenesis we established site-directed covalent crosslinking as a principle to detect interacting proteins of PTPs, and to study the effect of the interaction on the biological activity and regulation of the PTP (Pavic et al., ACS Chem. Biol. 2014).
The lab combines the expertise of molecular biologists and organic chemists opening up new ways to approach challenges in phosphatase research, and broadening the views and skills of every lab member.
Future projects and goals
- Understand the role of PRLs and inhibit them in oncogenesis.
- Further the development of chemical methods to use peptides and inositides as phosphatase modulators inside cells.
- Design modulators for the highly complex serine/threonine phosphatases.
- Continue to develop and maintain DEPOD.