What effect does the Ca²⁺-calmodulin complex typically mediate in the cell?

The Ca²⁺-calmodulin complex plays a critical role in cellular signaling by activating or inhibiting protein kinases. When calcium ions (Ca²⁺) bind to calmodulin, it undergoes a conformational change that allows it to interact with various target proteins, including protein kinases. This interaction can lead to the phosphorylation of specific serine or threonine residues on proteins, which effectively alters their activity and plays a key role in many signaling pathways involved in various cellular processes.

In contrast, while the complex may have indirect effects on gene expression by influencing kinases that modify transcription factors, its primary and direct action is the modulation of protein kinases. The Ca²⁺-calmodulin complex does not generally increase cell membrane permeability, nor does it play a direct role in facilitating cellular respiration. Thus, the focus on its function in regulating protein kinase activity highlights the significance of this complex in cellular signaling and functional outcomes.