Phospholipases: Structural and functional motifs for working at an interface

Phospholipases form a ubiquitous class of enzymes optimized to catalyze the hydrolysis of phospholipids. Because their products are often second messengers, they are highly regulated by the cell. For a given ester bond, there are separate secreted as well as cytoplasmic phospholipases with different substrate specificities and. modes of regulation. As it becomes available, structural information provides a view of interfacial catalysis for several of these phospholipases on a molecular level, Recent structural advances include solution structures of a pancreatic phospholipase A(2) in the absence and presence of a micellar interface, crystal structures of a bacterial phosphatidylinosiol-phospholipase C whose active site is reminiscent of ribonuclease, and a Ca2+ Lipid binding domain with high homology to regions in several cytoplasmic phospholipases that can model the way those proteins interact with the membrane surface. Phospholipases also have a wide and complex array of regulatory mechanisms involving cytoplasmic proteins, notably G-proteins, as well as different effector lipids (e.g., phosphatidylinositol-4,5-biphosphate, or PIP2) or Ca2+. Deconvolution of these interactions is necessary to understand their roles in different signal transduction pathways.