Molecular Underpinnings of Postsynaptic Calmodulin-dependent Calcium Signaling*

Calcium (Ca²⁺) signaling is a dynamic system where Ca²⁺ concentration fluctuates in range of 0.1-10μM with time. These short transient Ca²⁺ around the entry sites activate Ca²⁺-binding proteins such as calmodulin (CaM).  The prototypical pathway describes CaM as encoding a Ca²⁺ signal by selectively activating downstream CaM-dependent proteins through molecular binding.  However, CaM’s intrinsic Ca²⁺-binding properties alone appear insufficient to decode rapidly fluctuating Ca²⁺ signals.  It has been proposed that the temporally varying mechanism for producing target selectivity requires CaM-target interactions that directly tune the Ca²⁺-binding properties of CaM through reciprocal interactions.  In this presentation, I will focus on the binding mechanism of CaM and its target, which requires mutually and conformationally-induced changes in both participants   Then, I will focus on two unique and distinct CaM binding targets, neurogranin (Ng) and CaM-dependent kinase II (CaMKII), which are abundant in postsynaptic neuronal cells and are biochemically known to tune CaM’s affinity for Ca²⁺ in opposite directions.  My group has employed an integrative approach of quantum mechanical calculations, all-atomistic molecular dynamics, and coarse-grained molecular simulations to investigate the molecular mechanisms of CaM’s reciprocal interaction between target binding and Ca²⁺binding.  The research of my group has been driven and tested in close collaboration with experimentalists.  I will also discuss about CaM binding and target selection in the context of evolution and in a crowded environment.