Measurement of Cross-Relaxation between Amide Protons in ~(15)N-Enriched Proteins with Suppression of Spin Diffusion

摘要

A variant of two-dimensional nuclear Overhauser effect spectroscopy (NOESY) is described which allows one to observe cross-relaxation pathways between protons that have hetero-nuclear scalar couplings to nitrogen-15 or carbon-13. In ~(15)N-enriched proteins, it is possible to focus attention on Overhauser effects between amide protons that are due to a direct one-step transfer of longitudinal magnetization, e.g. I-(H_n~N) -> I-(H_(n+1)~N), while eliminating two-step spin-diffusion pathways such as I-(H_(n+1)~N) ->I-(H_(n~a) -> I-(Hn+1)~N). This can be achieved by selective inversion of the longitudinal magnetization of all amide protons that are scalar-coupled to ~(15)N in the middle of the relaxation time tau_m. Selective inversion can be obtainedby inserting a "bilinear rotation decoupling" (BIRD) pulse sandwich in tau_m.