Formation of intermolecular and intramolecular hydrogen bonds in histidine-binding protein J of Salmonella typhimurium upon binding l-histidine : A proton nuclear magnetic resonance study

Histidine-binding protein J of Salmonella typhimurium has been chosen as a model system for a proton nuclear magnetic resonance spectroscopic investigation of binding protein-ligand interaction. This interaction is involved in the recognition step of the osmotic shock-sensitive active transport systems. When J protein binds l-histidine, four new, low-field, exchangeable proton resonances appear in the region +7 to +12 parts per million downfield from the water proton resonance (or +11.7 to +16.7 parts per million downfield from the methyl proton resonance of 2,2-dimethyl-2-silapentane-5-sulfonate). Due to their chemical shift range and other properties, they indicate the formation of both intra- and intermolecular hydrogen bonds. Experiments with 15N-labeled compounds confirm this conclusion. The specificity of the hydrogen-bond formation is demonstrated by observing the effects of substrate analogs, temperature, pH, and mutations on the exchangeable proton resonances. Proton-proton nuclear Overhauser effect measurements suggest that two of these exchangeable proton resonances (at +7.2 and +10.6 parts per million from H 2O) are most likely from intramolecular hydrogen-bonded protons, while the other two (at +7.1 and +9.5 parts per million from H 2O) are intermolecular hydrogen bonds. Our finding of l-histidine-induced hydrogen-bond formation in histidine-binding protein J in the solution state is an excellent demonstration of the production of specific conformational changes in a periplasmic binding protein upon binding of ligand.