Improved HSQC experiments for the observation of exchange broadened signals.

We present here HSQC experiments with improved sensitivity for signals in the presence of exchange broadening. During periods of coherence transfer through scalar coupling the experiments employ CPMG-derived pulse trains to reduce loss of dephasing of spin coherence due to chemical exchange. (15)N-(1)H gradient CPMG-HSQC and SE-CPMG-HSQC experiments have been developed and applied to complexes of lac repressor headpiece with operator DNA. Improved sensitivity is demonstrated for many protein backbone and side-chain resonances in the complex, markedly for signals of protons located at the protein-DNA interface. In addition, a significant increase in intensity is observed for arginine guanidino groups undergoing conformational exchange.