BPS2026 – Deep sea osmolyte TMAO promotes phosphatidylethanolamine lipid intrinsic curvature, balancing the effect of pressure

Pressure reduces the magnitude of the spontaneous curvature of typical phosphatidylethanolamine (PE) lipids, due to the elevated local compressibility of the lipid’s hydrocarbon chains compared to the compressibility of the headgroup at the lipid/water interface. The deep ocean is subject to quite high pressures up to 1.1 kbar in the deepest trenches, and recent work has shown that some organisms adapted to the deep ocean produce lipids of high intrinsic curvature, effectively compensating for the effect of their habitat pressure. Separately, many deep-adapted animals have been shown to produce pressure-protective osmolytes such as trimethylamine N-oxide (TMAO) at high, depth-correlated concentrations. We hypothesized that these two adaptations might interact, i.e. that TMAO could increase the spontaneous curvatures of lipids and thus counteract the effect of pressure. Our pressure- and temperature-dependent X-ray diffraction measurements support this hypothesis, with 1 M TMAO counteracting the curvature effect of roughly 20 MPa of pressure, depending on the choice of lipid and temperature. We interpret this effect as an added interfacial tension at the lipid/water interface and present supporting thermodynamic measurements.