Relaxing the aquaporin crystal structure in a membrane with surface vibrational spectroscopy

TL;DR

This study combines vibrational spectroscopy and molecular dynamics to analyze aquaporin structures in native-like membranes, revealing differences from traditional X-ray crystallography data.

Contribution

It introduces a novel approach to study membrane protein structures in environments closer to their natural state, improving structural accuracy.

Findings

Detected significant structural differences between in situ and XRD structures of GlpF.

Demonstrated the effectiveness of vibrational spectroscopy combined with simulations for membrane protein analysis.

Provided insights into native membrane effects on aquaporin conformation.

Abstract

High-resolution structural information on membrane proteins is essential for understanding cell biology and for structure-based design of new medical drugs and drug delivery strategies. X-ray diffraction (XRD) can provide {\AA}ngstrom-level information about the structure of membrane proteins. Ideally protein structures should be solved in environments as close to the original biological context as possible. However, it is virtually impossible to crystallize proteins within the complex environment of a biological membrane. Instead, membrane proteins are typically transferred from their native membrane environment into detergent micelles, chemically stabilized and crystallized, all of which can compromise the conformation. This makes it imperative to develop alternative high-resolution techniques which are compatible with biological conditions. Here, we describe how a combina-tion of surface-sensitive vibrational spectroscopy in model membranes and molecular dynamics simulations can account for the native membrane environment. We observe the structure of glycerol facilitator channel (GlpF), an aquaporin membrane channel finely tuned to selectively transport water and glycerol molecules across the membrane barrier. We find subtle but significant differences between the XRD structure and the in-ferred in situ structure of GlpF.