A Highly Conserved Cysteine of Neuronal Calcium-sensing Proteins Controls Cooperative Binding of Ca2+ to Recoverin |
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Authors: | Matthew J Ranaghan Ramasamy P Kumar Kalyan S Chakrabarti Vanessa Buosi Dorothee Kern Daniel D Oprian |
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Institution: | From the ‡Department of Biochemistry and ;§Howard Hughes Medical Institute, Brandeis University, Waltham, Massachusetts 02454 |
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Abstract: | Recoverin, a 23-kDa Ca2+-binding protein of the neuronal calcium sensing (NCS) family, inhibits rhodopsin kinase, a Ser/Thr kinase responsible for termination of photoactivated rhodopsin in rod photoreceptor cells. Recoverin has two functional EF hands and a myristoylated N terminus. The myristoyl chain imparts cooperativity to the Ca2+-binding sites through an allosteric mechanism involving a conformational equilibrium between R and T states of the protein. Ca2+ binds preferentially to the R state; the myristoyl chain binds preferentially to the T state. In the absence of myristoylation, the R state predominates, and consequently, binding of Ca2+ to the non-myristoylated protein is not cooperative. We show here that a mutation, C39A, of a highly conserved Cys residue among NCS proteins, increases the apparent cooperativity for binding of Ca2+ to non-myristoylated recoverin. The binding data can be explained by an effect on the T/R equilibrium to favor the T state without affecting the intrinsic binding constants for the two Ca2+ sites. |
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Keywords: | Allosteric Regulation Calcium-binding Proteins Calcium Signaling Cooperativity Mutant Protein Myristoylation Cysteine Neuronal Calcium Sensor Sulfenic Acid |
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