A team of Research Resource investigators, including members of the labs of Joshua Sharp and Kelley Moremen, have worked together to help determine the role of glycosaminoglycans (GAGs) in nervous system development. GAGs bridge a complex of two proteins, Robo1 and Slit2, to help guide the development of axons in the nervous system. Using a combination of technologies, including MS and dynamic light scattering, the team was able to discover a new, low-affinity binding site for full-length heparin that appears to be important in signaling. The discovery of this second binding site allows us to provide a structural model for GAG-mediated signaling. The model shows a high-affinity shared heparin binding site between Robo1 and Slit2 responsible for stabilizing the complex, and a second low-affinity binding site that is important in transducing a signal through the rest of the Robo1 receptor.