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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).