The BEST-HMBC-HMQC experiment for pairing geminal methyl groups in Valine and Leucine side-chains.

Methyl groups are essential probes for characterising interactions and dynamics in large proteins. HN-based triple-resonance NMR experiments are often too insensitive for methyl assignments, making a NOESY-based approach an efficient strategy. Linking geminal methyl groups in leucine and valine residues is a crucial step in such NOESY-based methyl resonance assignment strategies. This link can be established unambiguously with the 3D-HMBC-HMQC experiment, introduced for large U-[12C2H] LV-[13CH3]2-labelled proteins. Here, we introduce the BEST variant of the 3D-HMBC-HMQC experiment which provides spectra with fewer artefacts arising from the water signal and a mean increase in signal-to-noise ratio per unit time of 16% compared to the original experiment with an optimised recovery delay and further gains when compared to more commonly used recovery delays in the range of 1.5-2 s.