Temperature effects on the hydrodynamic radius of the intrinsically disordered N-terminal region of the p53 protein

Intrinsically disordered proteins (IDPs) are often characterized in terms of the hydrodynamic radius, R-h. The R-h of IDPs are known to depend on fractional proline content and net charge, where increased numbers of proline residues and increased net charge cause larger R-h. Though sequence and charge effects on the R-h of IDPs have been studied, the temperature sensitivity has been noted only briefly. Reported here are R-h measurements in the temperature range of 5-75 degrees C for the intrinsically disordered N-terminal region of the p53 protein, p53(1-93). Of note, the R-h of this protein fragment was highly sensitive to temperature, decreasing from 35 angstrom at 5 degrees C to 26 angstrom at 75 degrees C. Computer generated simulations of conformationally dynamic and disordered polypeptide chains were performed to provide a hypothesis for the heat-induced compaction of p53(1-93) structure, which was opposite to the heat-induced increase in R-h observed for a model folded protein. The simulations demonstrated that heat caused R-h to trend toward statistical coil values for both proteins, indicating that the effects of heat on p53(1-93) structure could be interpreted as thermal denaturation. The simulation data also predicted that proline content contributed minimally to the native R-h of p53(1-93), which was confirmed by measuring R-h for a substitution variant that had all 22 proline residues changed for glycine. Proteins 2014; 82:668-678. (c) 2013 Wiley Periodicals, Inc.