15N−15N Proton Assisted Recoupling in Magic Angle Spinning NMR
Jzef R. Lewandowski†, Gal De Pape‡, Matthew T. Eddy and Robert G. Griffin*
We describe a new magic angle spinning (MAS) NMR experiment for obtaining 15N−15N 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, 15N−15N proton assisted recoupling (PAR), relies on a second-order mechanism, third spin assisted recoupling (TSAR), used previously in the context of 15N−13C and 13C−13C polarization transfer schemes. In comparison to 15N−15N proton-driven spin diffusion experiments, the PAR technique accelerates polarization transfer between 15N’s by a factor of 102−103 and is furthermore applicable over the entire range of currently available MAS frequencies (10−70 kHz).