The 2D {P-31} spin-echo-difference constant-time [C-13, H-1]-HMQC experiment for simultaneous determination of (3)J(H3 ' P) and (3)J(C4 ' P) in C-13-labeled nucleic acids and their protein complexes

A two-dimensional {P-31} spin-echo-difference constant-time [C-13, H-1]-HMQ C experiment (2D {P-31}-sedct-[C-13, H-1]-HMQC) is introduced for measureme nts of (3)J(C4'P) and (3)J(H3'P) scalar couplings in large C-13-labeled nuc leic acids and in DNA-protein complexes. This experiment makes use of the f act that H-1-C-13 multiple-quantum coherences in macromolecules relax more slowly than the corresponding C-13 single-quantum coherences. (3)J(C4'P) (3 )J(H3'P) are related via Karplus-type functions with the phosphodiester tor sion angles beta and epsilon, respectively, and their experimental assessme nt therefore contributes to further improved quality of NMR solution struct ures. Data are presented for a uniformly C-13, N-15-labeled 14-base-pair DN A duplex, both free in solution and in a 17-kDa protein-DNA complex. (C) 19 99 Academic Press.