Lipid Concentration Gradient Resulting from Shear Flow Advection of Membrane-Bound Proteins

Abstract

Flow mechanosensation sets many essential biological processes in motion. Under the right conditions, fluid flow can advect membrane-associated proteins with large extracellular domains. To explore these conditions we prepare a model system consisting of a discrete patch of supported lipid bilayer formed by bursting a giant unilamellar vesicle onto a glass coverslip. The vesicles are composed of a mixture of lipids that exhibits liquid-ordered and liquid-disordered coexistence, and contain a small amount of monosialoganglioside (GM1), which binds fluorescent cholera toxin subunit B (CTB). When shear flow is used to form a concentration gradient in CTB anchored to the bilayer, a corresponding lipid concentration gradient is created. Similar gradients of GM1 and associated lipids have been formed in supported bilayers previously using electrophoresis [1]. Since lipid composition in the two leaflets has been shown to be tightly coupled [2,3], a flow-induced lipid gradient provides a physical mechanism for transmitting a signal from the outer leaflet to the inner one.[1] Dynamic Reorganization and Correlation Among Lipid Raft Components. Monica M Lozano, Jennifer S. Hovis, Frank R. Moss III, and Steven G. Boxer, Journal of the American Chemical Society, 138, 9996-10001(2016).[2] Tuning lipid mixtures to induce or suppress domain formation across leaflets of unsupported asymmetric bilayers. Marcus D. Collins and Sarah L. Keller. Proceedings of the National Academy of the Sciences of the United States of America 105 (1) 124-128 (2007).[3] Transbilayer Colocalization of Lipid Domains Explained via Measurement of Strong Coupling Parameters. Matthew C. Blosser, Aurelia R. Honerkamp-Smith, Tao Han, Mikko Haataja, Sarah L. Keller. Biophysical Journal 109 (11) p2317-2327 (2015).