Molecular Dynamics Study of a Protein Motif that Senses Packing Defects Induced by Membrane Curvature

Abstract

A large number of biological processes, such as protein trafficking, are regulated by motifs that guide proteins to curved membranes. These unstructured motifs in solution fold into an amphipathic alpha-helix at the membrane interface. One of them is the ALPS (Amphipathic Lipid Packing Sensor) motif of the ArfGAP1 protein involved in uncoating of COPI vesicles. Bigay et al. proposed in 2003 that ALPS does not recognize curvature per se but rather packing defects that arise from membrane bending.Here, we performed molecular dynamics simulations to characterize lipid packing defects and understand how ALPS recognizes these defects. First, we show that packing defects can occur by introducing conical lipids such as dioleoylglycerol (DOG) into a flat phosphatidylcholine bilayer. Interestingly, the size and number of defects resemble those observed in a convex membrane by Voth and colleagues. Second, we observe that ALPS binding to the bilayer interface is driven by the insertion of bulky hydrophobic residues into large pre-existing packing defects. Remarkably, these defects do not co-localize with DOG lipids and are evenly distributed. To gain insight into the futher steps (folding into an alpha-helix), we are currently performing Replica-Exchange Molecular Dynamics simulations.JoAlle Bigay, Pierre Gounon, Sylviane Robineau & Bruno Antonny. 2003. Lipid packing sensed by ArfGAP1 couples COPI coat disassembly to membrane bilayer curvatures. Letters to Nature. 426.Haosheng Cui, Edward Lyman & Gregory A. Voth. 2011. Mechanism of Membrane Curvature Sensing by Amphipathic Helix Containing Proteins. Biophysical Journal. 100: 1271–1279.