3D NMR spectroscopy for resonance assignment and structure elucidation of proteins under MAS: novel pulse schemes and sensitivity considerations

Two types of 3D MAS NMR experiments are introduced, which combine standard (NC,CC) transfer schemes with (H-1,H-1) mixing to Simultaneously detect connectivities and Structural constraints Of uniformly N-15, C-13-labeled proteins with high spectral resolution. The homonuclear CCHHC and CCC experiments are recorded with one double-quantum evolution dimension in order to avoid a cubic diagonal in the spectrum. Depending oil the second transfer step, spin systems or proton-proton contacts can be determined with reduced spectral overlap. The heteronuclear NHHCC experiment encodes NH-HC proton-proton interactions, which are indicative for the backbone conformation of the protein. The third dimension facilitates the identification of the amino acid spin system. Experimental results on U-[N-15, C-13]valine and U-[N-15, C-13]ubiquitin demonstrate their usefulness for resonance assignments and for the determination of structural constraints. Furthermore. we give a detailed analysis of alternative multidimensional sampling schemes and their effect on sensitivity and resolution. (C) 2004 Elsevier Inc. All rights reserved.