Role of calcium in membrane interactions by PI(4,5)P₂-binding proteins

Ca²⁺ and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂] are key agents in membrane-associated signalling events. Their temporal and spatial regulation is crucial for activation or recruitment of proteins in the plasma membrane. In fact, the interaction of several signalling proteins with PI(4,5)P₂ has been shown to be tightly regulated and dependent on the presence of Ca²⁺, with co-operative binding in some cases. In these proteins, PI(4,5)P₂ and Ca²⁺ binding typically occurs at different binding sites. In addition, several PI(4,5)P₂-binding proteins are known targets of calmodulin (CaM), which, depending on the presence of calcium, can compete with PI(4,5)P₂ for protein interaction, translating Ca²⁺ transient microdomains into variations of PI(4,5)P₂ lateral organization in time and space. The present review highlights different examples of calcium-dependent PI(4,5)P₂-binding proteins and discusses the possible impact of this dual regulation on fine-tuning of protein activity by triggering target membrane binding in the presence of subtle changes in the levels of calcium or PI(4,5)P₂.