High resolution 1H NMR of a lipid cubic phase using a solution NMR probe

Area of Science:

• Biophysical chemistry
• Structural biology
• Materials science

Background:

• The monoacylglycerol/water cubic mesophase is crucial for membrane protein crystallization (in meso crystallogenesis).
• Understanding molecular interactions within this phase is key for optimizing crystallization strategies.
• Conventional NMR spectroscopy often lacks the resolution needed to probe these interactions at a molecular level.

Purpose of the Study:

• To develop an enhanced NMR method for high-resolution analysis of the cubic mesophase.
• To investigate the interactions of additives like L-tryptophan and rubipy within the cubic mesophase.
• To elucidate the localization and binding behavior of these additives relative to the lipid bilayer and aqueous channels.

Main Methods:

• Development of an improved NMR spectroscopy technique for enhanced spectral resolution using a conventional solution-state NMR probe.
• Acquisition of high-resolution one-dimensional (1D) and two-dimensional (2D) 1H NMR spectra of the cubic-Ia3d phase of hydrated monoolein.
• Analysis of chemical shift changes for L-tryptophan and rubipy upon transfer from aqueous solution to the cubic mesophase.

Main Results:

• The new NMR methodology yielded well-resolved J-coupling multiplets in 1D spectra and a high-resolution 2D t-ROESY spectrum.
• L-tryptophan exhibited specific interactions with the lipid bilayer interface, indicated by significant chemical shift differences.
• Ruthenium-tris(2,2-bipyridyl) dichloride (rubipy) was found to reside within the aqueous channels, showing no association with the lipid bilayer.

Conclusions:

• The developed NMR technique significantly enhances spectral resolution for studying lipid-based mesophases.
• L-tryptophan interacts favorably with the hydrophobic interface of the monoolein cubic mesophase.
• Rubipy remains soluble in the aqueous phase of the cubic mesophase, distinct from the lipidic environment.