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Inactivation of EF-hands makes GCAP-2 (p24) a constitutive activator of photoreceptor guanylyl cyclase by preventing a Ca2+-induced "activator-to-inhibitor" transition.
- Source :
-
The Journal of biological chemistry [J Biol Chem] 1996 Aug 09; Vol. 271 (32), pp. 19346-50. - Publication Year :
- 1996
-
Abstract
- Guanylyl cyclase activator proteins GCAP-1 and GCAP-2 (Dizhoor et al. , 1995, Gorczyca et al., 1995) are members of a recently identified subclass of EF-hand type Ca2+-binding proteins that respond to Ca2+ differently than any other known members of the EF-hand superfamily. GCAPs acquire an activating conformation only in their Ca2+-free form. Free Ca2+ concentrations corresponding to levels in dark-adapted vertebrate photoreceptors inhibit the ability of GCAPs to activate photoreceptor guanylyl cyclases (RetGCs). We studied the effects of mutations that block binding of Ca2+ to the EF-hands of GCAP-2. Unlike other EF-hand proteins, which fail to activate their target when their EF-hands are inactivated by mutations, GCAP-2 with any single EF-hand inactivated remains active and is 3-6 times less sensitive to the inhibitory effect of Ca2+. Inactivation of any two or all three EF-hands produces active forms of GCAP-2 that are insensitive to inhibition by physiological intracellular concentrations of Ca2+. Unexpectedly we also found that activation of RetGCs by a Ca2+-insensitive mutant is inhibited by Ca2+-loaded wild type GCAP-2. We propose the following. 1) GCAP-2 can exist in two extreme functional forms: an apo form that activates RetGCs and a Ca2+-loaded form that blocks activation of RetGCs. 2) All three EF-hands of GCAP-2 contribute to the inhibitory effect of Ca2+. 3) Inactivation of two or three EF-hands is sufficient to shift the "activator-inhibitor" transition outside the physiological range of intracellular free Ca2+.
- Subjects :
- Amino Acid Sequence
Animals
Binding Sites
Calcium-Binding Proteins genetics
Cattle
Cell Line
DNA, Complementary
Enzyme Activation
Guanylate Cyclase-Activating Proteins
Molecular Sequence Data
Mutagenesis
Rats
Sequence Homology, Amino Acid
Calcium metabolism
Calcium-Binding Proteins metabolism
Guanylate Cyclase metabolism
Photoreceptor Cells enzymology
Subjects
Details
- Language :
- English
- ISSN :
- 0021-9258
- Volume :
- 271
- Issue :
- 32
- Database :
- MEDLINE
- Journal :
- The Journal of biological chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 8702620
- Full Text :
- https://doi.org/10.1074/jbc.271.32.19346