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

A two-dimensional [31P] spin-echo-difference constant-time [13C, 1H]-HMQC experiment (2D [31P]-sedct-[13C, 1H]-HMQC) is introduced for measurements of 3J(C4'P) and 3J(H3'P) scalar couplings in large 13C-labeled nucleic acids and in DNA-protein complexes. This experiment makes use of the fact that 1H-13C multiple-quantum coherences in macromolecules relax more slowly than the corresponding 13C single-quantum coherences. 3J(C4'P) and 3J(H3'P) are related via Karplus-type functions with the phosphodiester torsion angles beta and epsilon, respectively, and their experimental assessment therefore contributes to further improved quality of NMR solution structures. Data are presented for a uniformly 13C, 15N-labeled 14-base-pair DNA duplex, both free in solution and in a 17-kDa protein-DNA complex. Copyright 1999 Academic Press.