What Wnts are a group of extensively studied signaling molecules with great importance for human survival and well-being, where defects in Wnt signaling can lead to cancer and neurodegenerative disorders such as Alzheimer’s disease. Wnt signaling is highly complex, and Wnts interact with several intra- and extracellular molecules on their journey to exerting their effects. Recent studies have shown that binding to extracellular polysaccharides known as glycosaminoglycans (GAGs) is crucial for Wnts to relay their signals, and that this binding is dependent on sulfate groups distributed along the GAG chains. Sulfate groups on GAGs are arranged in patterns, and the structure of these patterns decide which Wnts the GAGs can bind to, and how strongly they bind. Why The specific sulfation patterns required for Wnt binding to GAGs are unknown, and this gap in knowledge is hampering the study of Wnts. Uncovering of GAGs carrying sulfation patterns with high affinity for Wnts would permit pioneering examination of the structure of Wnt-GAG complexes, and is important for gaining a more complete view of how GAGs may regulate Wnt signaling. These studies may further open up for discovery of GAGs as Wnt signaling modifiers, which could potentially be used for treatment of patients suffering from cancer and neurodegenerative diseases. How For identification of GAG structures responsible for binding to individual Wnts, I will apply a unique library of cell lines, where each cell displays distinct different GAG profiles. Using this library, Wnt affinity for specific GAGs will be determined through cell-based binding assays. The intricate molecular details of Wnt-GAG complexes will then be examined by state-of-the-art methods for structural studies, cryo electron microscopy and x-ray crystallography. I will further test selected GAG structures for their ability to influence Wnt signaling in excitatory or inhibitory manners using cell-based Wnt signaling assays.