Spectral editing: selection of methyl groups in multidimensional solid-state magic-angle spinning NMR

Abstract

A simple spectroscopic filtering technique is presented that may aid the assignment of ¹³C and ¹⁵N resonances of methyl-containing amino-acids in solid-state magic-angle spinning (MAS) NMR. A filtering block that selects methyl resonances is introduced in two-dimensional (2D) ¹³C-homonuclear and ¹⁵N–¹³C heteronuclear correlation experiments. The 2D ¹³C–¹³C correlation spectra are recorded with the methyl filter implemented prior to a ¹³C–¹³C mixing step. It is shown that these methyl-filtered ¹³C-homonuclear correlation spectra are instrumental in the assignment of C_δ resonances of leucines by suppression of C_γ–C_δ cross peaks. Further, a methyl filter is implemented prior to a ¹⁵N–¹³C transferred-echo double resonance (TEDOR) exchange scheme to obtain 2D ¹⁵N–¹³C heteronuclear correlation spectra. These experiments provide correlations between methyl groups and backbone amides. Some of the observed sequential ¹⁵N–¹³C correlations form the basis for initial sequence-specific assignments of backbone signals of the outer-membrane protein G.