Ligand-binding domain of membrane bound guanylyl cyclases
Ligand-binding domain of membrane bound guanylyl cyclases (GCs), which are known to be activated by sperm-activating peptides (SAPs), such as speract or resact. These ligand peptides are released by a range of invertebrates to stimulate the metabolism and motility of spermatozoa and are also potent chemoattractants. These GCs contain a single transmembrane segment, an extracellular ligand binding domain, and intracellular protein kinase-like and cyclase catalytic domains. GCs of insect and nematodes, which exhibit high sequence similarity to the speract receptor are also included in this model.