Concepts and Methods of Solid-State NMR Spectroscopy Applied to Biomembranes

Concepts of solid-state NMR spectroscopy and applications to fluid membranes are reviewed in this paper. Membrane lipids with ²H-labeled acyl chains or polar head groups are studied using ²H NMR to yield knowledge of their atomistic structures in relation to equilibrium properties. This review demonstrates the principles and applications of solid-state NMR by unifying dipolar and quadrupolar interactions and highlights the unique features offered by solid-state ²H NMR with experimental illustrations. For randomly oriented multilamellar lipids or aligned membranes, solid-state ²H NMR enables <i>direct</i> measurement of residual quadrupolar couplings (RQCs) due to individual C–²H-labeled segments. The distribution of RQC values gives nearly complete profiles of the segmental order parameters <i>S</i>_CD^(<i>i</i>) as a function of acyl segment position (<i>i</i>). Alternatively, one can measure residual dipolar couplings (RDCs) for natural abundance lipid samples to obtain segmental <i>S</i>_CH order parameters. A theoretical mean-torque model provides acyl-packing profiles representing the cumulative chain extension along the normal to the aqueous interface. Equilibrium structural properties of fluid bilayers and various thermodynamic quantities can then be calculated, which describe the interactions with cholesterol, detergents, peptides, and integral membrane proteins and formation of lipid rafts. One can also obtain direct information for membrane-bound peptides or proteins by measuring RDCs using magic-angle spinning (MAS) in combination with dipolar recoupling methods. Solid-state NMR methods have been extensively applied to characterize model membranes and membrane-bound peptides and proteins, giving unique information on their conformations, orientations, and interactions in the natural liquid-crystalline state

Additional file 1: of EMSAR: estimation of transcript abundance from RNA-seq data by mappability-based segmentation and reclustering

Supplementary Material. (PDF 250 kb

Visualization 2

A video of a single set of 20 sub-frames capturing retinal vasculature under vertical illumination. The image acquisition rate is 10,000 fps. The playback rate is 10 fps

visualization2.tif

Photoreceptor images of N3 at 3° TR captured by (a) the AO-pcMSO system with an illumination fill factor of 0.11 (Fig. 5(a)) and (b) our previously reported AO-cSLO system (Fig. 5(b)), marking cones visible in both images. (c) Normalized radial power spectrum of photoreceptor images for N3 at 3° TR. The scale bar is 10 μm

Visualization 9

A video of phase contrast images of N3 at 5° T 0.15° SR, cross-correlation maps, and plots of measured velocities and cross-correlation values. The image acquisition rate is 500 fps. Playback rate is 30 fps

Visualization3.avi

A video of phase contrast images of N1 at 3.5° T 2° SR and corresponding normalized cross-correlation maps. The image acquisition rate is 500 fps. The playback rate is 30 fps

Supplementary document for High-speed, phase contrast retinal and blood flow imaging using an adaptive optics partially confocal multi-line ophthalmoscope - 6864115.pdf

Supplemental Figure

Visualization 5

A video of a set of partially confocal vascular images of N1 at 6.6° T 2° SR. The image acquisition rate is 500 fps. The playback rate is 60 fps

visualization3.tif

Retinal images of N3 at 4° NR focused on photoreceptor layer, retinal vessel, and nerve fiber layer, respectively, with illumination fill factors of (a)-(c) 1, (d)-(f) 0.25, and (g)-(i) 0.11. The grayscale is adjusted for each image so that the top 0.05% of pixels are saturated and pixels equal or lower than 25% of the upper limit are set to zero. The scale bar is 20 µm

Visualization 7

A video of a set of vascular phase contrast images of N3 at 6.3° T 2.75° IR obtained with horizontal line illumination. The image acquisition rate is 500 fps. The playback rate is 60 fps