Biophysical Society Thematic Meeting - October 13-15, 2015

Biophysics of Proteins at Surfaces: Assembly, Activation, Signaling

Wednesday Speaker Abstracts

Membrane Curvature Enables N-Ras Lipid Anchor Sorting to Liquid-ordered Membrane Phases Jannik B. Larsen 1 , Martin B. Jensen 1 , Vikram K. Bhatia 1 , Søren L. Pedersen 1 , Thomas Bjørnholm 1 , Lars Iversen 1 , Mark Uline 2 , Igal Szleifer 3 , Knud J. Jensen 1 , Nikos S. Hatzakis 1 , Dimitrios Stamou 1 . 1 University of Copenhagen, Copenhagen, Denmark, 2 University of South Carolina, Columbia, NC, USA, 3 Northwestern University, Evanston, IL, USA. In vivo observations have suggested that the trafficking and sorting of membrane-anchored Ras GTPases are regulated by partitioning between distinct sphingolipid-sterol membrane domains. However, in vitro experiments have not been able to recapitulate such partitioning between liquid ordered (lo)/liquid disordered (ld) phases (I), suggesting that more complex physical principles influence Ras sorting into membrane domains in vivo. We employed our single liposome assay 1 to study the recruitment by membrane curvature of the minimal anchor of the N-Ras isoform for ld or lo phase-state systems. This confocal microscopy based study revealed membrane curvature as a novel modulator of N-Ras lipid anchor partitioning (II) and that membrane curvature was essential for enrichment in raft-like lo phase (III). 2 Additionally we used microscopic molecular theory to elucidate that the curvature dependent lo enrichment was driven by increased relief of the lateral pressure in curved lo versus ld membranes. 2 Ordered phases and curvature often coexist in vivo and recruit lipidated proteins, i.e. in trafficking vesicles or caveolae invaginations. Our results suggest that membrane curvature can allow cells to regulate lateral partitioning of lipidated proteins into such ordered membrane domains.

1. Hatzakis, N.S. et al. Nat. Chem. Biol. 5, 835-841 (2009). 2. Larsen, J.B. et al. Nat. Chem. Biol. 11, 192-194 (2015).

24