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Ca2+ signaling and Target Binding Regulations: Calmodulin and Centrin In Vitro and In Vivo

Juan Martinez-Sanz, Dora Grecu and Liliane Assairi

Changes in Ca2+ concentrations act as a second messenger to regulate biological processes. Ca2+ sensor proteins transduce these Ca2+ signals upon binding to protein targets that are involved in the cellular process that is being regulated.

Ca2+ sensor proteins such as calmodulin and centrin bind Ca2+ through acidic residues that compose the EFhand motifs and further bind targets via surfaces that recognize specific motifs on targets. However, in some cases, the binding of a Ca2+ sensor protein to a target can occur in the absence of Ca2+. Upon Ca2+ binding, Ca2+-sensor proteins undergo conformational changes, which lead to the exposure of surface that interacts with target. Moreover, Ca2+ binding and the binding of Ca2+ sensors to targets induce conformational changes that drive regulation. Comparisons of the Ca2+-sensor proteins calmodulin and centrin provide information on regulatory processes.