Molecular Basis of the Interaction between Signaling Lipids and Proteins; the Special Case of Phosphatidic Acid

Abstract

Intricate networks of signaling cascades regulate cellular development and response to environmental factors. within these cascades, the lipid second messenger phosphatidic acid (PA) is an important regulator in all eukaryotes. Rapid but transient increase of PA levels regulate growth, acclimatization and survival during development and stress response. Signaling lipids, including PA, function by selectively recruiting proteins to the membrane. This facilitates either the activation or inhibition of these target proteins. However, the exact details of phospholipid-mediated stress response mechanisms are still largely unclear, partially due to the lack of characterized target proteins of PA.Here we report on characterization of the interaction between various regulatory proteins and lipid second messengers by determining their lipid binding specificity and affinity for PA. Furthermore, to assess relative binding affinity in variable structural lipid environments, in vitro liposome-binding assays with liposomes covering a range of lipid compositions are performed. In our binding studies, phosphatidylethanolamine is utilized to study the role of membrane curvature and electrostatics in lipid-binding.Specific attention is given to the electrostatic/hydrogen bond switch model. Hydrogen bond formation between basic amino acids and the PA phosphomonoester headgroup increases the negative charge of PA and allows for docking of the protein binding domain. The elucidation of the mechanism behind the binding of proteins to lipid second messengers such as PA will further develop our understanding of their function in plant growth and stress responses. This in turn can help in understanding regulation and cell functioning in numerous organisms.