The use of TROSY for detection and suppression of conformational exchange NMR line broadening in biological macromolecules

The interference between conformational exchange-induced time-dependent variations of chemical shifts in a pair of scalar coupled 1H and 15N spins is used to construct novel TROSY-type NMR experiments to suppress NMR signal loss in [15N,1H]-correlation spectra of a 14-mer DNA duplex free in solution and complexed with the Antp homeodomain. An analysis of double- and zero-quantum relaxation rates of base 1H-15N moieties showed that for certain residues the contribution of conformational exchange-induced transverse relaxation might represent a dominant relaxation mechanism, which, in turn, can be effectively suppressed by TROSY. The use of the new TROSY method for exchange-induced transverse relaxation optimization is illustrated with two new experiments. 2D h1J(HN),h2J(NN) quantitative [15N,1H]-TROSY to measure h1J(HN) and h2J(NN) scalar coupling constants across hydrogen bonds in nucleic acids, and 2D (h2J(NN) + h1J(NH))-correlation-[15N,1H]-TROSY to correlate 1H(N) chemical shifts of bases with the chemical shifts of the tertiary 15N spins across hydrogen bonds using the sum of the trans-hydrogen bond coupling constants in nucleic acids.