Practice question

Resact peptide binding to receptor guanylate cyclase on sperm flagellum activates cGMP synthesis opening K+ channels and triggering Ca2+ oscillations critical for chemotactic steering. Electrophysiology and genomics identified cation channel of sperm, CatSper, as major Ca2+ entry route mediating oscillations. CatSper genes encode four homologous subunits forming pH-sensitive channel enriched in flagellar principal piece. Sea urchin genome contains CatSper orthologs; blocking pore abolishes Ca2+ influx and turning. Bindin, resact and hyalin encode adhesion proteins unrelated to conductance. Thus calcium channels activated by resact are encoded by CatSper genes.