Pressure dependent elastic constants of membranes

Environments like the deep sea are characterized by low temperature (near freezing) and high pressure, with pressure increasing by 1 bar for every 10 m depth. This presents a substantial challenge for cell membranes because the membrane is the most pressure-sensitive material in the cell, with a compressibility ten times that of a folded soluble protein. Recently, Winnikoff, et al. showed that a class of invertebrates called ctenophores synthesize an extraordinary amount of plasmalogen to adapt to the high pressure of the deep ocean and suggest a “homeocurvature” mechanism — ctenophores adjust their lipidomes to maintain critical material properties within a narrow range, to preserve deformability at high pressure. Here, we use high-pressure (Hi-P) MD simulations to systematically study the pressure dependence of plasmalogens, comparing the spontaneous curvature under pressure of ester, ether, and plasmalogen-linked phospholipids. A comparison with Hi-P SAXS measurements suggests that ester and ether lipids have a qualitatively correct pressure dependence. At the same time, simulations of the plasmalogen membranes show that the monolayer is too flat compared to the others. Here, we consider several explanations, including the pressure dependence of headgroup hydration and the conformational landscape of the plasmalogen linkage.