A pH-dependent conformational change of staphylococcal nuclease: hydrogen-1 two-dimensional nuclear Overhauser...

Two-dimensional nuclear magnetic resonance (2d-NMR) dipolar correlation spectroscopy (NOESY) for the calcium binding protein, staphylococcal nuclease, was used to study the conformations in solution as a function of pH. A series of 2d-NOESY spectra of the nuclease H124L-Ca(++)-thymidine 3'5'-bisphosphate ternary complex demonstrated significant pH dependent changes: NOE cross peaks between 46His delta H and an aliphatic proton at 2.66 ppm appeared at pH 10.2, but not at pH 5.5. Some other NOE cross peaks between aromatic and aliphatic protons displayed chemical shift changes in omega 2 or both dimensions (omega 1, omega 2). These results indicated that a local rearrangement accompanies the ionization of the functional groups and has a role in enzyme function.