Biomolecular solid-state NMR spectroscopy at highest field: the gain in resolution at 1200 MHz

Abstract

Progress in NMR in general and in biomolecular applications in particular is driven by increasing magnetic-field strengths leading to improved resolution and sensitivity of the NMR spectra. Recently, persistent superconducting magnets at a magnetic field strength (magnetic induction) of 28.2 T corresponding to 1200 MHz proton resonance frequency became commercially available. We present here a collection of high-field NMR spectra of a variety of proteins, including molecular machines, membrane proteins and viral capsids and others. We show this large panel in order to provide an overview over a range of representative systems under study, rather than a single best performing model system. We discuss both carbon-13 and proton-detected experiments, and show that in 13C spectra substantially higher numbers of peaks can be resolved compared to 850 MHz while for 1H spectra the most impressive increase in resolution is observed for aliphatic side-chain resonances.

Proton Detected Solid-State NMR of Membrane Proteins at 28 Tesla (1.2 GHz) and 100 kHz Magic-Angle Spinning

“…In each case, we compare the spectra taken from a single fully protonated sample packed in a 0.7 mm rotor and recorded at a 950 MHz spectrometer, and at a 1200 MHz spectrometer. A variety of samples including fibrils, capsids, and membrane proteins are currently the subject of a similar comparison between 850 MHz and 1200 MHz [58].…”

Paramagnetic spin labeling of a bacterial DnaB helicase for solid-state NMR

“…Because the dipolar relaxation of a nucleus in one DnaB monomer is the combined effect of all 24 spin labels in DnaB dodecamer, the effective distance in equation ( 4) is evaluated by the sum of r -6 distances to the Gd 3+ or O1 centers of mass of all 24 spin label sites. In addition, the distances to both DnaB carbon atoms, which contribute to the same NMR cross peak, are included in the summation in equation (4). Note that because the conformations of chains A and B in the DnaB crystal structure are not identical (Cα-RMSD is 4.6 Å over 72% of the residues), r -6 averaging of the distances calculated for chains A and B is additionally applied in equation ( 4).…”

“…Solid-state NMR spectroscopy represents a versatile tool for the structural characterization of proteins as well as for probing their conformational dynamics [1,2]. Technical advances in solid-state NMR spectroscopy, such as the availability of high magnetic-field strengths [3,4], high rotation frequencies in magic-angle spinning (MAS) experiments [5,6] as well as the development of highly efficient multidimensional radiofrequency pulse sequences, have enabled the routine assignment of uniformly 13 C- 15 N labeled proteins with molecular weights up to ~30 kDa [7], and determination of the structures of small to medium-sized proteins (<100-150 amino acids per symmetric monomer). Structure determination mostly relies on the collection of a large number of distance restraints extracted from dipolar coupling-based NMR experiments and backbone torsion-angle restraints derived from the chemical shifts, e.g.…”

“…Collection of long-range restraints (with |i-j| >4), with small Dij values, requires recording spectra with long mixing times. While for large proteins signal overlap in the spectra recorded at long mixing times can become problematic, the resolution can be improved in these cases by going to higher dimensions or by increasing the external magnetic-field strength [3,4].…”

Field and magic angle spinning frequency dependence of proton resonances in rotating solids

“…Clearly, an MAS frequency of 110 kHz MAS is not sufficient to overcome the dipolar coupling network [34] among protons in the complete absence of chemical dilution. Therefore, the quest for higher MAS frequencies continues [35,36]. However, increasing MAS frequency forces the use of smaller rotor volumes, translating into a smaller number of spins and reduced absolute sensitivity.…”