Assignment of backbone resonances for larger proteins using the C-13-H-1 coherence of a H-1(alpha)-, H-2-, C-13-, and N-15-labeled sample

A suite of triple resonance NMR experiments for the assignment of backbone resonances of a larger protein using selectively H-1(alpha) labeling to a sample uniformly labeled with C-13, N-15, and H-2 is described. The relaxation time of H-1(alpha)-C-13(alpha) zero/double quantum coherence was more than 4 times as long as that of C-13(alpha) Single quantum coherence. Three-dimensional HACAN, HACACB, HACACO, and HACA(N)CO experiments were newly designed to utilize selectively labeled H-1(alpha) nuclei. HACAN provides intraresidue and sequential connectivities through amide N-15 spins. HACACO and HACA(N)CO provide intraresidue and sequential connectivities through (CO)-C-13 spins. (H)ACACB provides connectivity to C-13(beta), giving the type of amino acid. Long-life H-1(alpha)-C-13(alpha) zero/double quantum coherence provides high sensitivity in these NMR experiments. Except for a few amino acid type-specific problems, all sequential connectivities were obtained for a test sample of a 98 amino acid protein at 10 degrees C, which rotationally diffuses with a correlation time of 17 ns, corresponding to an over 30 kDa protein at 30-40 degrees C. Zero/double quantum based triple resonance experiments and H-1(alpha) selective labeling provide a new approach for NMR studies on larger proteins.