Ca2+differently affects hydrophobic properties of guanylyl cyclase-activating proteins (GCAPs) and recoverin.

Guanylyl cyclase-activating proteins (GCAPs) and recoverin are retina-specific Ca2+-binding proteins involved in phototransduction. We provide here evidence that in spite of structural similarities GCAPs and recoverin differently change their overall hydrophobic properties in response to Ca2+. Using native bovine GCAP1, GCAP2 and recoverin we show that: i) the Ca2+-dependent binding of recoverin to Phenyl-Sepharose is distinct from such interactions of GCAPs; ii) fluorescence intensity of 1-anilinonaphthalene-8-sulfonate (ANS) is markedly higher at high [Ca2+]gfree (10 μM) than at low [Ca2+]free (10 nM) in the presence of recoverin, while an opposing effect is observed in the presence of GCAPs; iii) fluorescence resonance energy transfer from tryptophane residues to ANS is more efficient at high [Ca2+]free in recoverin and at low [Ca2+]free in GCAP2. Such different changes of hydrophobicity evoked by Ca2+ appear to be the precondition for possible mechanisms by which GCAPs and recoverin control the activities of their target enzymes.