title: Lipid-assisted protein transport: A diffusion-reaction model supported by kinetic experiments and molecular dynamics simulations.
abstract: The protein transport inside a cell is a complex phenomenon that goes through several difficult steps. The facilitated transport requires sophisticated machineries involving protein assemblies. In this work, we developed a diffusion-reaction model to simulate co-transport kinetics of proteins and lipids. We assume the following: (a) there is always a small lipid concentration of order of the Critical Micellar Concentration (CMC) in equilibrium with the membrane; (b) the binding of lipids to proteins modulates the hydrophobicity of the complexes and, therefore, their ability to interact and merge with the bilayer; and (c) some lipids leave the bilayer to replenish those bound to proteins. The model leads to a pair of integral equations for the time-evolution of the adsorbed proteins in the lipid bilayer. Relationships between transport kinetics, CMC, and lipid-protein binding constants were found. Under particular conditions, a perturbation analysis suggests the onset of kinks in the protein adsorption kinetics. To validate our model, we performed leakage measurements of vesicles composed by either high or low CMC lipids interacting with Islet Amyloid PolyPeptide (IAPP) and Aβ (1-40) used as sample proteins. Since the lipid-protein complex stoichiometry is not easily accessible, molecular dynamics simulations were performed using monomeric IAPP interacting with an increasing number of phospholipids. Main results are the following: (a) 1:1 lipid-protein complexes generally show a faster insertion rate proportional to the complex hydrophobicity and inversely related to lipid CMC; (b) on increasing the number of bound lipids, the protein insertion rate decreases; and
authors.affiliation: Department of Chemical Science, University of Catania, Viale A. Doria 6, I-95125 Catania, Italy.
authors.forename: Carmelo
authors.initials: C
authors.lastname: La Rosa
authors.affiliation: Department of Chemical Science, University of Catania, Viale A. Doria 6, I-95125 Catania, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Scalisi
authors.affiliation: Department of Chemical Science, University of Catania, Viale A. Doria 6, I-95125 Catania, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Lolicato
authors.affiliation: Department of Physics, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Martina
authors.initials: M
authors.lastname: Pannuzzo
authors.affiliation: Department of Chemical Science, University of Catania, Viale A. Doria 6, I-95125 Catania, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Raudino
mesh_terms: D000327:Adsorption; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D055459:Facilitated Diffusion; D005452:Fluoresceins / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D058228:Islet Amyloid Polypeptide / Q000737:chemistry*; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry*; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D010446:Peptide Fragments / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D011485:Protein Binding; D021381:Protein Transport
chemical_list: D016229:Amyloid beta-Peptides; D005452:Fluoresceins; D058228:Islet Amyloid Polypeptide; D008051:Lipid Bilayers; D010446:Peptide Fragments; D010713:Phosphatidylcholines; C078592:amyloid beta-protein (1-40); C024098:6-carboxyfluorescein; C066558:dinervonylphosphatidylcholine; D004134:Dimyristoylphosphatidylcholine