Introduction to Proton Detection in Biological Samples under Ultra-Fast Magic Angle Spinning

Protons are characterized by having a natural abundance of more than 99.9 %, as well as a high gyromagnetic ratio. These attributes provide much greater detection sensitivity than those of 13C or 15N, making 1H-detected NMR spectroscopy very attractive, not just for solution NMR. Soluble samples benefit from the fact that unwanted dipolar couplings are cancelled out by molecular tumbling, a feature that insoluble molecules lack. As a result, a strong network of homonuclear proton dipolar couplings dramatically broadens the linewidth of any 1H signal in solid-state NMR. Two approaches especially have been shown to overcome this obstacle; sample preparation using perdeuteration- reprotonation to dilute the dense proton network, and the use of increased magic angle spinning (MAS) speeds in the order of 60 to 111 kHz (Figure 1). In collaboration with Guido Pintacuda and co-workers, Bruker BioSpin presents three basic 1H-detected pulse programs (‘pulprog’) that allow initial protein backbone assignment under fast MAS.

Venita Daebel
Bruker BioSpin GmbH, Rheinstetten, Germany

Figure 1 proton detection 01

Figure 1: (A) 2D 1H-detected hNH spectrum (blue) of a u-[13C,15N]-labeled and 100% 1H-back-exchanged SSB sample recorded within 30 min on a Bruker 1GHz spectrometer at 111 kHz MAS (Bruker 0.7 mm probe). (B) 2D 1H-detected hCαNH spectrum (red) of ubiquitin (same labeling scheme) recorded within 65 min on a Bruker 600 MHz spectrometer at 60 kHz MAS.