Removal of slow-pulsing artifacts in in-phase (15)N relaxation dispersion experiments using broadband (1)H decoupling

Understanding of the molecular mechanisms of protein function requires detailed insight into the conformational landscape accessible to the protein. Conformational changes can be crucial for biological processes, such as ligand binding, protein folding, and catalysis. NMR spectroscopy is exquisitely sensitive to such dynamic changes in protein conformations. In particular, Carr–Purcell–Meiboom–Gill (CPMG) relaxation dispersion experiments are a powerful tool to investigate protein dynamics on a millisecond time scale. CPMG experiments that probe the chemical shift modulation of (15)N in-phase magnetization are particularly attractive, due to their high sensitivity. These experiments require high power (1)H decoupling during the CPMG period to keep the (15)N magnetization in-phase. Recently, an improved version of the in-phase (15)N-CPMG experiment was introduced, offering greater ease of use by employing a single (1)H decoupling power for all CPMG pulsing rates. In these experiments however, incomplete decoupling of off-resonance amide (1)H spins introduces an artefactual dispersion of relaxation rates, the so-called slow-pulsing artifact. Here, we analyze the slow-pulsing artifact in detail and demonstrate that it can be suppressed through the use of composite pulse decoupling (CPD). We report the performances of various CPD schemes and show that CPD decoupling based on the 90(x)–240(y)–90(x) element results in high-quality dispersion curves free of artifacts, even for amides with high (1)H offset. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s10858-018-0193-2) contains supplementary material, which is available to authorized users.