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 var iations of chemical shifts in a pair of scalar coupled H-1 and N-15 spins i s used to construct novel TROSY-type NMR experiments to suppress NMR signal loss in [N-15,H-1]-correlation spectra of a 14-mer DNA duplex free in solu tion and complexed with the Antp homeodomain. An analysis of double- and ze ro-quantum relaxation rates of base H-1-N-15 moieties showed that for certa in 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 fo r exchange-induced transverse relaxation optimization is illustrated with t wo new experiments, 2D (h1)J(HN),(h2)J(NN)-quantitative [N-15,H-1]-TROSY to measure (h1)J(HN) and (h2)J(NN) scalar coupling constants across hydrogen bonds in nucleic acids, and 2D ((h2)J(NN)+(h1)J(NH))-correlation-[N-15,H-1] -TROSY to correlate H-1(N) chemical shifts of bases with the chemical shift s of the tertiary N-15 spins across hydrogen bonds using the sum of the tra ns-hydrogen bond coupling constants in nucleic acids.