Thursday, April 9, 2009, Condensed Matter Biological Physics Seminar, Tobias Baumgart, Department of Chemistry, University of Pennsylvania, "On the Sorting of Lipids and Proteins in Membrane Curvature and Composition Gradients", 4:30 PM, Doherty Hall A310, CMU
 

Abstract:

Biological membranes consist of wealth of lipids and proteins forming quasi two-dimensional mixtures. Cellular membranes differ in composition and shape both laterally and also comparing various organelles. Non-ideal, i.e. non-random mixing of these components is expected, and can be amplified by thermodynamic variables such as composition and temperature, as well as by mechanical means to control membrane curvature. I will present three aspects of complex membrane mixtures. First, I will demonstrate how molecular details of signaling protein membrane anchors influence the association of these anchors with laterally inhomogeneous membranes. Second, I will discuss a variety of measurements to determine phase boundary (line) tension in membranes with fluid phase coexistence. Finally, I will present our recent findings on protein and lipid sorting among regions with varying membrane curvature. We investigate to what extent lipids and proteins are sorted based on their intrinsic molecular shape, and also investigate how non-ideal mixing properties of membrane mixtures can be amplified by applying membrane curvature gradients. Experimental results of protein partitioning in membrane curvature gradients are examined by means of statistical mechanical models. Our results contribute to a quantitative understanding of the biophysical principles underlying cellular membrane sorting.