Structure of Gel Phase DPPC Determined by X-ray Diffraction

TL;DR

This study uses advanced X-ray diffraction techniques to elucidate the detailed structure of DPPC lipid bilayers in the gel phase, revealing interdigitated hydrocarbon chains and providing insights into monolayer coupling.

Contribution

It introduces a new high-resolution X-ray data set and a refined structural model of DPPC gel phase, highlighting interdigitation of hydrocarbon chains and coupling mechanisms.

Findings

Hydrocarbon chains from opposing monolayers are mini-interdigitated.

Strong coupling exists between monolayers regarding chain tilt directions.

New structural features are identified that can be validated by simulations.

Abstract

High resolution low angle x-ray data are reported for the gel phase of DPPC lipid bilayers, extending the previous q range of 1.0 {\AA}-1 to 1.3 {\AA}-1, and employing a new technique to obtain more accurate intensities and form factors |F(q)| for the highest orders of diffraction. Combined with previous wide angle x-ray and volumetric data, a space filling model is employed to obtain gel phase structure at a mesoscopic level. A new conclusion from this analysis is that the hydrocarbon chains from opposing monolayers are mini-interdigitated; this would help explain the previously well-established result that the opposing monolayers are strongly coupled with respect to their chain tilt directions. Even more detailed structural features are described that have not been obtained from experiment but that could, in principle, be obtained from simulations that would first be validated by agreement with the wide angle and the new low angle |F(q)| x-ray data.