Technical Highlight - April 2009
Short description: Achieving solution structures of proteins that produce NMR spectra with a high degree of signal overlap will be easier with a new approach to NMR data acquisition.Angewandte Chemie 48, 1479-1483 (2009)
NMR spectroscopy is widely used for solving protein structures, but a structure is only as good as the spectrum from which it is obtained. Membrane proteins in particular have proved difficult to solve by NMR, but a new and generally applicable technique looks likely to pave the way to many new structures.
A variety of approaches have been taken to achieve what is called 'pure absorptive mode signal detection'. This is because absorptive frequency domain signals are much narrower than non-absorptive signals. Hence, 'clean' absorption mode data acquisition, where signals are not superimposed on residual, broader non-absorptive signal components, is critical for maximizing spectral resolution. In real life, however, NMR signals often have residual non-absorptive signal components that until now could not be removed. This ultimately results in both lower spectral resolution and a shift in the position of the NMR signal. This has a knock on effect to how precisely chemical shift can be measured and may impede NMR signal assignment within the spectrum.
Wu et al., supported by PSI NESG, report a general method for clean absorption mode signal detection. This approach relies on phase-shifted mirrored time domain sampling (PMS). The basic idea of such mirrored sampling is to sample the evolution in the time domain twice; that is once forward from time 0 to time +t and then backward from time 0 to time −t. Linear combination of the two data sets results, after transformation into the frequency domain, in a spectrum with signals devoid of any non-absorptive components.
They tested their technique with a PSI NESG target protein, a 8 kDa protein. As they predicted, applying PMS produced the desired clean absorption mode spectra.
The new technique solves a long-standing problem for NMR data acquisition and is likely to be widely used in NMR-based research in science and engineering.
Y. Wu, A. Ghosh & T. Syzperski Clean absorption-mode NMR data acquisition.
Angewandte Chemie 48, 1479-1483 (2009).