[superscript 15]N-[superscript 15]N Proton Assisted Recoupling in Magic Angle Spinning NMR

Abstract

We describe a new magic angle spinning (MAS) NMR experiment for obtaining [superscript 15]N−[superscript 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, [superscript 15]N−[superscript 15]N proton assisted recoupling (PAR), relies on a second-order mechanism, third spin assisted recoupling (TSAR), used previously in the context of [superscript 15]N−[superscript 13]C and [superscript 13]C−[superscript 13]C polarization transfer schemes. In comparison to [superscript 15]N−[superscript 15]N proton-driven spin diffusion experiments, the PAR technique accelerates polarization transfer between [superscript 15]N’s by a factor of ~10[superscript 2]−10[superscript 3] and is furthermore applicable over the entire range of currently available MAS frequencies (10−70 kHz).