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Instead of Binding Calcium, One of the EF-hand Structures in Guanylyl Cyclase Activating Protein-2 Is Required for Targeting Photoreceptor Guanylyl Cyclase
Journal article   Peer reviewed

Instead of Binding Calcium, One of the EF-hand Structures in Guanylyl Cyclase Activating Protein-2 Is Required for Targeting Photoreceptor Guanylyl Cyclase

Alexandre N. Ermilov, Elena V. Olshevskaya and Alexander M. Dizhoor
The Journal of biological chemistry, v 276(51), pp 48143-48148
21 Dec 2001
PMID: 11584009
url
https://doi.org/10.1074/jbc.M107539200View
Published, Version of Record (VoR) Open

Abstract

Guanylyl cyclaseactivator proteins (GCAPs) are calcium-binding proteins closely related to recoverin, neurocalcin, and many other neuronal Ca2+-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 Ca2+ concentrations, the activator form of GCAP-2 associates into a dimer, which dissociates when GCAP-2 binds Ca2+ 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 Ca2+-sensitive dimerization. Point mutations within the EF-1 region can interfere with both the activation of the cyclase by the Ca2+-free form of GCAP-2 and the inhibition of retGC basal activity by the Ca2+-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 Ca2+ for the ability to interact with the target enzyme.

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Biochemistry & Molecular Biology
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