Multiplet component separation for measurement of methyl 13C-1H dipolar couplings in weakly aligned proteins

A simple spectral editing procedure is described that generates separate subspectra for the methyl 13C-[1H3] multiplet components of 1H-13C HSQC spectra. The editing procedure relies on co-addition of in-phase and antiphase spectra and yields 1H-coupled constant-time HSQC subspectra for the methyl region that have the simplicity of the regular decoupled CT-HSQC spectrum. Resulting spectra permit rapid and reliable measurement of 1H-13C J and dipolar couplings. The editing procedure is illustrated for a Ca2+-calmodulin sample in isotropic and liquid crystalline phases.