High Affinity Binding to Profilin by a Covalently Constrained, Soluble Mimic of Phosphatidylinositol-4,5-bisphosphate Micelles

Phosphoinositide (PI) lipids are essential regulators of a wide variety of cellular functions. We present here the preparation of a multivalent analogue of a phosphatidylinositol-4,5-bisphosphate (PIP₂) micelle containing only the polar headgroup portion of this lipid. We show that this dendrimer binds to the cytoskeletal protein profilin with an affinity indistinguishable from that of PIP₂, despite the fact that profilin discriminates between PIP₂ and its monomeric hydrolysis product inositol-1,4,5-triphosphate (IP₃) under physiological conditions. These data demonstrate that the diacylglycerol (DAG) moiety of PIP₂ is not required for high-affinity binding and suggest that profilin uses multivalency as a key means to distinguish between the intact lipid and IP₃. The class of soluble membrane analogues described here is likely to have broad applicability in the study of protein·PI interactions.