What enables calmodulin to interact with a variety of proteins when bound with Ca²⁺?

Calmodulin is a calcium-binding messenger protein that undergoes a conformational change upon the binding of Ca²⁺ ions. When calcium ions are bound, calmodulin's shape changes, allowing it to interact effectively with a range of target proteins, including kinases, phosphatases, and other regulatory proteins. This structural alteration creates specific binding sites that facilitate the interaction with various proteins, enabling calmodulin to modulate numerous cellular processes.

The ability to bind to diverse proteins is primarily due to this change in shape rather than changes in concentration, size, or charge. These other factors do not directly contribute to calmodulin's functional versatility in signal transduction pathways. The flexibility resulting from the shape change is crucial for calmodulin’s role in transmitting calcium signals within cells.