Structural effects of Mg2Â + on the regulatory states of three neuronal calcium sensors operating in vertebrate phototransduction

Our results confirmed that Mg2 + is unable to trigger the typical Ca2 +-induced conformational change of recoverin (myristoyl switch) while it decreases its thermal stability. Interestingly, Mg2 + seems to affect the conformation of GCAP2 both at high and low [Ca2 +], however the variations are more substantial for myristoylated GCAP2 in the absence of Ca2 +. GCAP1 is responsive to Mg2 + only in its low [Ca2 +] state and Mg2 +-GCAP1 tertiary structure slightly differs from both apo and Ca2 +-bound states. Finally, MD simulations suggest that the GCAP1 state harboring one Mg2 + ion bound to EF2 acquires structural characteristics that are thought to be relevant for the activation of the guanylate cyclase. Moreover, all the putative Mg2 +-bound states of myristoylated GCAP1 are structurally less flexible than Ca2 +-bound states. GCAP1 acquires a more compact tertiary structure that is less accessible to the solvent, thereby inducing a different conformation to the myristoyl moiety, which might be crucial for the activation of the guanylate cyclase. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.