Local structure involving histidine-12 in reduced S-sulfonated ribonuclease A detected by proton NMR spectroscopy under folding conditions.
The C epsilon H proton resonance of His-12 of reduced cysteine S-sulfonated bovine pancreatic ribonuclease A exhibits a nonlinear temperature dependence of the chemical shift in its 1H-NMR spectrum at an apparent pH of 3.0. At temperatures below ca. 35 degrees C, the temperature dependence of the chemical shift of the His-12 C epsilon H resonance is opposite in sign to those of His-48, His-105, and His-119. At temperatures above ca. 35 degrees C, the temperature dependence of the chemical shift of the His-12 C epsilon H resonance is similar to those of the other three His C epsilon H resonances. These data indicate the existence of an equilibrium between locally ordered and locally disordered environments of His-12 in the sulfonated protein at temperatures below ca. 35 degrees C. The ordered and disordered conformations interconvert at a rate that is fast relative to the 1H-NMR chemical shift time scale--i.e., the locally ordered structure has a lifetime of much less than 7 msec. These results demonstrate that short- and medium-range interactions can define short-lived local structures under conditions of temperature and solution composition at which the native protein structure is stable. Furthermore, they demonstrate the utility of reduced derivatives of disulfide-containing proteins as model systems for the identification of local structures that may play a role as early-forming chain-folding initiation structures.
D000818:Animals; D002417:Cattle; D006639:Histidine; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction; D010179:Pancreas / Q000201:enzymology; D011487:Protein Conformation; D012259:Ribonuclease, Pancreatic / Q000032:analysis*; D013451:Sulfonic Acids; D013696:Temperature
D013451:Sulfonic Acids; D006639:Histidine; D012259:Ribonuclease, Pancreatic