Dimerization of Guanylyl Cyclase-activating Protein and a Mechanism of Photoreceptor Guanylyl Cyclase Activation

doi:10.1074/jbc.274.36.25583

Dimerization of Guanylyl Cyclase-activating Protein and a Mechanism of Photoreceptor Guanylyl Cyclase Activation*

From the ^‡Department of Ophthalmology/Kresge Eye Institute and ^§Department of Pharmacology, Wayne State University School of Medicine, Detroit, Michigan 48201

Abstract

Ca²⁺-binding guanylyl cyclase-activating proteins (GCAPs) stimulate photoreceptor membrane guanylyl cyclase (retGC) in the light when the free Ca²⁺concentrations in photoreceptors decrease from 600 to 50 nm. RetGC activated by GCAPs exhibits tight dimerization revealed by chemical cross-linking (Yu, H., Olshevskaya, E., Duda, T., Seno, K., Hayashi, F., Sharma, R. K., Dizhoor, A. M., and Yamazaki, A. (1999) J. Biol. Chem. 274, 15547–15555). We have found that the Ca²⁺-loaded GCAP-2 monomer undergoes reversible dimerization upon dissociation of Ca²⁺. The ability of GCAP-2 and its several mutants to activate retGC in vitro correlates with their ability to dimerize at low free Ca²⁺ concentrations. A constitutively active GCAP-2 mutant E80Q/E116Q/D158N that stimulates retGC regardless of the free Ca²⁺ concentrations forms dimers both in the absence and in the presence of Ca²⁺. Several GCAP-2/neurocalcin chimera proteins that cannot efficiently activate retGC in low Ca²⁺concentrations are also unable to dimerize in the absence of Ca²⁺. Additional mutation that restores normal activity of the GCAP-2 chimera mutant also restores its ability to dimerize in the absence of Ca²⁺. These results suggest that dimerization of GCAP-2 can be a part of the mechanism by which GCAP-2 regulates the photoreceptor guanylyl cyclase. The Ca²⁺-free GCAP-1 is also capable of dimerization in the absence of Ca²⁺, but unlike GCAP-2, dimerization of GCAP-1 is resistant to the presence of Ca²⁺.

Footnotes

↵* This work was supported by National Eye Institute Grant EY11522 (to A. M. D.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¶ Recipient of a career development award from Research to Prevent Blindness. To whom correspondence should be addressed: Dept. of Ophthalmology/Kresge Eye Institute, Wayne State University School of Medicine, 4717 St. Antoine, Detroit, MI 48201. Tel.: 313-577-1573; Fax: 313-577-7635; E-mail: adizhoor@med.wayne.edu.
Abbreviations:

retGC

photoreceptor membrane guanylyl cyclase

GCAP

guanylyl cyclase-activating protein
- Received May 19, 1999.
- Revision received July 1, 1999.
The American Society for Biochemistry and Molecular Biology, Inc.