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Biophysics of Proteins at Surfaces: Assembly, Activation, Signaling
Poster Abstracts
16-POS
Board 16
Ceramide Increases Free Volume Voids in DPPC Membranes
Felix Goni
, Eneko Axpe, Aritz B. Garcia-Arribas, Jon I. Mujika, Alicia Alonso, Jesus M.
Ugalde, Fernando Plazaola.
Universidad del Pais Vasco, Leioa, Spain.
Positron annihilation lifetime spectroscopy (PALS) can measure changes in local free
volume voids in lipid bilayers. PALS has been applied, together with differential scanning
calorimetry (DSC) and molecular dynamics (MD) simulations, to study free volume voids in
DPPC and DPPC : ceramide (85 : 15 mol : mol) model membranes in the 20–60 °C range. The
free volume void average size clearly increases with the gel–fluid phase transition of the lipid, or
lipid mixture. Ceramide increases void size at all temperatures, particularly in the range causing
the gel–fluid transition of the mixture. A parallel study of PALS and calorimetric data indicates
that, for the complex thermotropic transition of the DPPC–ceramide mixture, PALS is detecting
the transition of the DPPC component, while calorimetry changes indicate mainly the melting of
the ceramide-enriched domains. Molecular dynamics calculations provide a clear distinction
between ceramide-rich and poor domains, and show that the voids are predominantly located
near the membrane nodal plane. The ceramide-induced increase in void volume size occurs as
well at temperatures when both phospholipid and ceramide are in the fluid state, indicating that
the effect is not the result of phospholipid–ceramide domain coexistence. The above
observations may be related to hitherto unexplained properties of ceramide, such as the increase
in membrane permeability, and the induction of transmembrane (flip-flop) lipid motion.
19-POS
Board 19
Phospholipase C ß1 Induces Membrane Tubulation in a Phosphatidylethanolamine-
dependent Manner.
Takehiko Inaba
1
, Takuma Kishimoto
1
, Takuya Tajima
2
, Shota Sakai
1
, Mitsuhiro Abe
1
,
Motohide Murate
1
, Asami Makino
1
, Nario Tomishige
1
, Reiko Ishitsuka
1
, Shinji Takeoka
2
,
Toshihide Kobayashi
1
.
1
RIKEN, Wako, Saitama, Japan,
2
Waseda Univ, Shinjuku, Tokyo, Japan.
Lipid membrane curvature plays important roles in various physiological phenomena. Using
darkfield microscopy, we performed non-biased screening of a protein that induces deformations
of non-labeled liposomes. We identified that phospholipase C ß1 (PLCß1) induces tubulation of
the liposome containing phosphatidylethanolamine and phosphatidylserine. Interestingly, the
characteristic C-terminal sequence of PLCß1, but not the conserved regions of PH domain or
catalytic domains, is essential for the tubulation of liposomes. Our results indicate that hybrid
structure of PLCß1 controls its enzyme activity through sensing and/or modulation of the
membrane curvature by the C-terminal domains.