Figure 5: Guanylate cyclase C: extracellular domain is responsible for ligand binding. Juxtamembrane domain is located near the cell membrane and it is responsible for binding the G-proteins. Kinase homology domain needs to be phosphorylated for pronounced guanylate cyclase activity. Catalytic domain converts GTP to cGMP after ligand binding to extracellular domain. C-terminal tail of the GC-C is unique and it is involved in binding the GC-C to cytoskeleton.