Intrinsic Differences in Backbone Dynamics between Wild Type and DNA-Contact Mutants of the p53 DNA Binding Domain Revealed by Nuclear Magnetic Resonance Spectroscopy

Mutations in p53's DNA binding domain (p53DBD) are associated with 50% of all cancers, making it an essential system to investigate and understand the genesis and progression of cancer. In this work, we studied the changes in the structure and dynamics of wild type p53DBD in comparison with two of its hot-spot DNA-contact mutants, R248Q and R273H, by analysis of backbone amide chemical shift perturbations and 15N spin relaxation measurements. The results of amide chemical shift changes indicated significantly more perturbations in the R273H mutant than in wild type and R248Qp53DBD. Analysis of 15N spin relaxation rates and the resulting nuclear magnetic resonance order parameters suggests that for most parts, the R248Q mutant exhibits limited conformational flexibility and is similar to the wild type protein. In contrast, R273H showed significant backbone dynamics extending up to its beta-sandwich scaffold in addition to motions along the DNA binding interface. Furthermore, comparison of rotational correlation times between the mutants suggests that the R273H mutant, with a higher correlation time, forms an enlarged structural fold in comparison to the R248Qmutant and wild type p53DBD. Finally, we identify three regions in these proteins that show conformational flexibility to varying degrees, which suggests that the R273H mutant, in addition to being a DNA-contact mutation, exhibits properties of a conformational mutant.