The 2D { ³¹ P} Spin-Echo-Difference Constant-Time [ ¹³ C, ¹ H]-HMQC Experiment for Simultaneous Determination of ³ J _H3′P and ³ J _C4′P in ¹³ C-Labeled Nucleic Acids and Their Protein Complexes

A two-dimensional { ³¹ P} spin-echo-difference constant-time [ ¹³ C, ¹ H]-HMQC experiment (2D { ³¹ P}-sedct-[ ¹³ C, ¹ H]-HMQC) is introduced for measurements of ³ J _C4′P and ³ J _H3′P scalar couplings in large ¹³ C-labeled nucleic acids and in DNA-protein complexes. This experiment makes use of the fact that ¹ H- ¹³ C multiple-quantum coherences in macromolecules relax more slowly than the corresponding ¹³ C single-quantum coherences. ³ J _C4′P and ³ J _H3′P are related via Karplus-type functions with the phosphodiester torsion angles β and ∈, respectively, and their experimental assessment therefore contributes to further improved quality of NMR solution structures. Data are presented for a uniformly ¹³ C, ¹⁵ N-labeled 14-base-pair DNA duplex, both free in solution and in a 17-kDa protein-DNA complex.