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Methyl ¹H SQ-CPMG experiment

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You can get the example files from the GitHub ChemEx page.

This example demonstrates the application of methyl ¹H SQ-CPMG experiment (cpmg_ch3_1h_sq) for studying 13CH3-labeled methyl groups. It allows measuring ¹H Δϖ while still preserving the methyl-TROSY effects.1 The sensitivity is much higher than older experiments for similar purposes.2 This experiment can be combined with MQ-CPMG experiment (cpmg_ch3_mq) such that Δϖ for both ¹³C and ¹H can be obtained simultaneously.

In this experiment signals from both I = 3/2 and I = 1/2 manifolds are collected, to get rid of potential artifacts due to off-resonance effects CPMG pulses are applied with XY-4 phase cycle. Besides, each CPMG pulse can be applied as 90x240y90x composite variety to achieve even better off-resonance performance, which is indicated by comp180_flg. To get flat relaxation dispersion profiles in the absence of a chemical exchange process, relaxation compensation pulses should be applied and ncyc_max should be set properly.

In this example, a selective set of residues are used for obtaining global parameters (pB and kex) first, and then residue-specific parameters for each residue are obtained with global parameters fixed.

Footnotes​

  1. T. Yuwen, R. Huang, P. Vallurupalli, and L. E. Kay. A Methyl-TROSY-Based ¹H Relaxation Dispersion Experiment for Studies of Conformational Exchange in High Molecular Weight Proteins Angew. Chem. Int. Ed. 58, 6250-6254 (2019). https://doi.org/10.1002/anie.201900241 ↩

  2. V. Tugarinov2007, and L. E. Kay. Separating Degenerate ¹H Transitions in Methyl Group Probes for Single-Quantum 1H-CPMG Relaxation Dispersion NMR Spectroscopy J. Am. Chem. Soc. 129, 9514-9521 (2007). https://doi.org/10.1021/ja0726456 ↩