Calmodulin, a Calcium-binding protein, that mediates Ca2+ signaling is involved in all types of cellular mechanisms, including metabolism, synaptic plasticity, nerve growth, smooth muscle contraction, etc.
Proteins, such as neurogranin that plays a vital role in postsynaptic function, however, can bind to calmodulin in Ca2+-free or Ca2+-bound state via their IQ calmodulin-binding motifs.
Studies have proven that calmodulin's affinity for Ca2+ increases when it is bound to a calmodulin-binding protein, which allows for it to take on its regulatory role for Ca2+-dependent reactions.
[4] Found in the nervous system, GAP-43 is a growth-associated protein (GAP) expressed in high levels during presynaptic developmental and regenerative axonal growth.
When there are low levels of Ca2+ concentrations, GAP-43 is able to bind and stabilize the inactive Ca2+-free state of calmodulin, this allows it to absorb and reversibly inactivate the CaM in the growth cones.