From structure to function: Understanding how Wnts binding to their multiple receptors

• Applicant: Dr. Anselm Sommer
• Subject Area: Biochemistry ; Biophysics ; Structural Biology ; Cell Biology
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 412008255

Wnt proteins are crucial signaling molecules that coordinate many aspects of development through a variety of cell surface receptors including: 10 different 7-transmembrane-domain Frizzleds (Fzs), 5 receptor tyrosine kinases (RTKs), and other co-receptors. Wnt signaling defects underlie several diseases, including cardiovascular disorders and cancers. A major goal for understanding the complex world of Wnt signaling is to decipher which Wnt protein(s) bind(s) to which receptors, and how this binding is defined. Most is known about beta-catenin-dependent, or ‘canonical’ Wnt signaling, in which Wnts engage Fz proteins and LRP5/6 co-receptors – although mechanisms underlying receptor activation are not understood. Much less is understood about beta-catenin-independent (‘non-canonical’) Wnt pathways, which include the planar cell polarity pathway and Ca2+-dependent signaling. Non-canonical signaling is restricted to a subset of Wnts and receptors – including the RTKs and certain Fzs. The Wnt-binding RTKs are especially interesting, since 4 (of 5) have ‘dead’ or pseudo kinase domains.Although Wnt binding to a Fz cysteine-rich-domain (CRD) has been visualized crystallographically, it is not clear how Wnts bind any of their other receptors. Several studies also question the central role for Wnt acylation in Fz binding that is suggestion by the Wnt/Fz crystal structure. My proposed work focuses on understanding the multiple receptor-binding modes of Wnts and thus their mechanisms of receptor activation. I will investigate the structural basis of their binding to the RTK Wnt receptors. I will also test the hypothesis based on our preliminary studies that Wnt acylation regulates Wnt binding specifity and range – rather than just ‘docking’ the ligand on to its receptor. To achieve this, I will create and establish expression and purification strategies for Wnt proteins and their receptors using insect and mammalian expression systems and chromatographic purification strategies. I will analyze binding and signaling activities using biochemical and cellular approaches, and X-ray crystallography to visualize complex formation. I will then link the results of my structural and specificity experiments to biological outcome in cellular studies – using Wnts that I know activate specific receptor subsets. This work will substantially increase the knowledge of Wnt biology and will help to lay the foundations for future drug discovery for cardiovascular diseases and cancers.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Mark Lemmon, Ph.D.