Lipid signaling is concentration dependent. Lipid effector proteins are unable to bind membranes when the concentration of their target lipid is low (left). Cellular signals lead to the activation of lipid-modifying enzymes, which generate target lipids that can then recruit the effector proteins to the membrane (right). Conversely, other cellular signals can activate enzymes that convert the target lipid back to its original form or to another lipid, causing release of the effector from the membrane. In this example, the target lipid highlighted in yellow is also cone-shaped (for example, PA, PE or DAG) in contrast to the majority of membrane lipids, which are cylindrical in shape (for example, PC and PS; headgroups colored brown). The conical shape reduces packing of lipid headgroups, which exposes the hydrophobic acyl layer surrounding the target lipid. This may facilitate insertion of hydrophobic amino acids and effector binding.