Neurogranin is the main postsynaptic protein regulating the availability of calmodulin, binding to it in the absence of calcium. Phosphorylation by protein kinase C lowers its binding ability.
In the context of synaptic function, neurogranin is the primary postsynaptic protein that controls calmodulin availability, binding to it in the absence of calcium ions. The phosphorylation of neurogranin by protein kinase C reduces its ability to bind calmodulin.