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Updated: Jul 16, 2026

Characterization of G Protein-coupled Receptors by a Fluorescence-based Calcium Mobilization Assay
Published on: July 28, 2014
Calcium-dependent conformational changes in guanylate cyclase-activating protein 2 monitored by cysteine
Andreas Helten1, Karl-Wilhelm Koch
1Biochemistry Group, IBU, Faculty V, University of Oldenburg, D-26111 Oldenburg, Germany.
Abstract:
Guanylate cyclase-activating protein 2 (GCAP2) is expressed in vertebrate photoreceptors cells where it regulates the activity of membrane bound guanylate cyclases in a Ca(2+)-dependent manner. The essential trigger step involves a Ca(2+)-induced conformational change in GCAP2. We investigated these Ca(2+)-dependent changes by probing the cysteine accessibility in wild type and mutant GCAP2 forms with the thiol-modifying reagent 5,5'-dithio-bis-(2-nitrobenzoic acid) (DTNB). Cysteine residues in position 35 and 111 displayed a restricted accessibility in the presence of Ca(2+), whereas cysteine in position 131 reacted with DTNB in the presence and absence of Ca(2+). Our data indicate that the Ca(2+)-sensitivity of GCAP2 is significantly controlled by its third Ca(2+)-binding site, EF-hand 3.
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