Decoupling of dipolar and hydrophobic motions in biological membranes

• Main Authors: Antila, Hanne S, Wurl, Anika, Ollila, O. H. Samuli, Miettinen, Markus S, Ferreira, Tiago M
• Format: Journal Article
• Language: English
• Published: 14-09-2020
• Subjects: Physics - Soft Condensed Matter
• DOI: 10.48550/arxiv.2009.06774

Cells use homeostatic mechanisms to maintain an optimal composition of
distinct types of phospholipids in cellular membranes. The hydrophilic dipolar
layer at the membrane interface, composed of phospholipid headgroups, regulates
the interactions between cell membranes and incoming molecules, nanoparticles,
and viruses. On the other hand, the membrane hydrophobic core determines
membrane thickness and forms an environment for membrane-bound molecules such
as transmembrane proteins. A fundamental open question is to what extent the
motions of these regions are coupled and, consequently, how strongly the
interactions of lipid headgroups with other molecules depend on the properties
and composition of the membrane hydrophobic core. We combine advanced
solid-state nuclear magnetic resonance spectroscopy methodology with
high-fidelity molecular dynamics simulations to demonstrate how the rotational
dynamics of choline headgroups remain nearly unchanged (slightly faster) with
incorporation of cholesterol into a phospholipid membrane, contrasting the well
known extreme slowdown of the other phospholipid segments. Notably, our results
suggest a new paradigm where phospholipid headgroups interact as quasi-freely
rotating flexible dipoles at the interface, independent of the properties in
the hydrophobic region.