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Powerful NMR

PSI-SGKB [doi:10.1038/th_psisgkb.2009.11]
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.

The scanning pre-initiation complex. (Left) Schematic representation of the pre-initiation complex on mRNA. The 5' cap of the mRNA (m7Gppp) and the start codon are shown. (Right) Model for the spatial orientation of the eIF4A helicase complex on the 40S ribosomal subunit. The polarity of mRNA and the direction of scanning are shown. In both figures, the three HEAT domains of eIF4G are colored red, orange and yellow. eIF4A (at the back) is light blue

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.

Maria Hodges

References

  1. Y. Wu, A. Ghosh & T. Syzperski Clean absorption-mode NMR data acquisition.
    Angewandte Chemie 48, 1479-1483 (2009).

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