Heteronuclear NMR spectroscopy of proteins encapsulated in cubic phase lipids

Lipidic cubic phases, which form spontaneously via the self-assembly of certain lipids in an aqueous environment, are highly prospective nanomaterials with applications in membrane protein X-ray crystallography and drug delivery. Here we report H-1-N-15 heteronuclear single/multiple quantum coherence (HSQC, HMQC) spectra of N-15-enriched proteins encapsulated in inverse bicontinuous lipidic cubic phases obtained on a standard commercial high resolution NMR spectrometer at ambient temperature. N-15-enriched proteins encapsulated in this lipidic cubic phase show: (i) no significant changes in tertiary structure, (ii) significantly reduced solvent chemical exchange of backbone amides, which potentially provides a novel concept for quantifying residue-specific hydration; and (iii) improved spectral sensitivity achieved with band-selective excitation short-transient (BEST) spectroscopy, which is attributed to the presence of an abundant source of H-1 nuclear spins originating from the lipid component of the cubic phase. (C) 2019 Elsevier Inc. All rights reserved.