~(15)N-~(15)N Proton Assisted Recoupling in Magic Angle Spinning NMR

摘要

We describe a new magic angle spinning (MAS) NMR experiment for obtaining ~(15)N-~(15)N correlation spectra. The approach yields direct information about the secondary and tertiary structure of proteins, including identification of α-helical stretches and interstrand connectivity in antiparallel β-sheets, which are of major interest for structural studies of membrane proteins and amyloid fibrils. The method, ~(15)N-~(15)N proton assisted recoupling (PAR), relies on a second-order mechanism, third spin assisted recoupling (TSAR), used previously in the context of ~(15)N-~(13)C and ~(13)C-~(13)C polarization transfer schemes. In comparison to ~(15)N-~(15)N proton-driven spin diffusion experiments, the PAR technique accelerates polarization transfer between ~(15)N's by a factor of ～10~2-10~3 and is furthermore applicable over the entire range of currently available MAS frequencies (10-70 kHz).