Instead of binding calcium, one of the EF-hand structures in guanylyl cyclase activating protein-2 is required for targeting photoreceptor guanylyl cyclase.
Guanylyl cyclase activator proteins (GCAPs) are calcium-binding proteins closely related to recoverin, neurocalcin, and many other neuronal Ca(2+)-sensor proteins of the EF-hand superfamily. GCAP-1 and GCAP-2 interact with the intracellular portion of photoreceptor membrane guanylyl cyclase and stimulate its activity by promoting tight dimerization of the cyclase subunits. At low free Ca(2+) concentrations, the activator form of GCAP-2 associates into a dimer, which dissociates when GCAP-2 binds Ca(2+) and becomes inhibitor of the cyclase. GCAP-2 is known to have three active EF-hands and one additional EF-hand-like structure, EF-1, that deviates form the EF-hand consensus sequence. We have found that various point mutations within the EF-1 domain can specifically affect the ability of GCAP-2 to interact with the target cyclase but do not hamper the ability of GCAP-2 to undergo reversible Ca(2+)-sensitive dimerization. Point mutations within the EF-1 region can interfere with both the activation of the cyclase by the Ca(2+)-free form of GCAP-2 and the inhibition of retGC basal activity by the Ca(2+)-loaded GCAP-2. Our results strongly indicate that evolutionary conserved and GCAP-specific amino acid residues within the EF-1 can create a contact surface for binding GCAP-2 to the cyclase. Apparently, in the course of evolution GCAP-2 exchanged the ability of its first EF-hand motif to bind Ca(2+) for the ability to interact with the target enzyme.
Ermilov
A N
AN
Department of Ophthalmology/Kresge Eye Institute, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
Olshevskaya
E V
EV
Dizhoor
A M
AM
D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002850:Chromatography, Gel; D006162:Guanylate Cyclase / Q000378:metabolism*; D051604:Guanylate Cyclase-Activating Proteins; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D011487:Protein Conformation; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D002135:Calcium-Binding Proteins; D051604:Guanylate Cyclase-Activating Proteins; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; C110715:guanylate cyclase 1; D006162:Guanylate Cyclase; D002118:Calcium