Impact of PI(3,4,5)P3-Mediated Beta-Arrestin-1 Recruitment on Structure of Asymmetric Lipid Bilayers

The membrane spanning G-protein coupled receptors (GPCRs) facilitate crucial physiological responses to a variety of extracellular ligands, such as hormones, neurotransmitters, ions, photons, and other stimuli [1], thus 50% of drugs available in the market today target GPCRs [2]. The biological mechanisms behind GPCR-signaling involves several other biomolecules, including the key protein group of β-arrestins. These cytosolic adaptor proteins regulate signaling through several different pathways, classically by removing receptors from the plasma membrane via clathrin-mediated endocytosis [3].In membrane binding experiments using both confocal fluorescence microscopy and quartz crystal microbalance, we found that β-arrestin-1 binds specifically to supported lipid bilayers (SLBs) containing phosphatidylinositol trisphosphate lipids, PI(3,4,5)P3. We have consistently shown, using both methods, that such binding is lipid specific and not driven by membrane charge. We have also shown that the membrane-protein interaction depends on protein concentration and membrane composition, and that β-arrestins can induce membrane curvature, which may play a role in the endocytic pathway. This is for the first time quantified with respect to dynamics and respective contributions of specific vs non-specific binding.Having established an assay for PI(3,4,5)P3-mediated recruitment of β-arrestin-1, we conducted a series of neutron reflection experiments to study the protein-lipid interaction on a structural level. Both hydrogenated and deuterated protein was used in reflectometry experiments with diverse contrast matching of the bulk media. We present here the detailed structures of asymmetric lipid bilayers containing PI(3,4,5)P3, and demonstrate that β-arrestin-1 not only binds but also reorganizes the membrane structure.1. Rosenbaum, D. M. et al. Nature. 459(7245), 356-363 (2009).2. Gudermann, T. et al. J Mol Med-Jmm. 73(2), 51-63 (1995).3. DeWire, S. M. et al. Annu Rev Physiol. 69, 483-510 (2007).