| Summary: | Submitted in the fulfillment of the requirement for the Degree of Master's in Chemistry, Durban University of Technology, 2017. === P53 is a tumour suppressor protein that is dysfunctional in most human cancer cells. Mutations in the p53 genes result in the expression of mutant proteins which accumulate to high levels in tumour cells. Several studies have shown that majority of the mutations are concentrated in the DNA-binding domain where they destabilize its conformation and eliminate the sequence- specific DNA-binding to abolish p53 transcription activities. Accordingly, this study involved an investigation of the effects of mutations associated with cancer, based on the framework of sequences and structures of p53 DNA-binding domains, analysed by SIFT, Pmut, I-mutant, MuStab, CUPSAT, EASY-MM and SDM servers. These analyses suggest that 156 mutations may be associated with cancer, and may result in protein malfunction, including the experimentally validated mutations. Thereafter, 54 mutations were further classified as disease- causing mutations and probably have a significant impact on the stability of the structure. The detailed stability analyses revealed that Val143Asp, Ala159Pro, Val197Pro, Tyr234Pro, Cys238Pro, Gly262Pro and Cys275Pro mutations caused the highest destabilization of the structure thus leading to malfunctioning of the protein. Additionally, the structural and functional consequences of the resulting highly destabilizing mutations were explored further using molecular docking and molecular dynamics simulations. Molecular docking results revealed that the p53 DNA-binding domain loses its stability and abrogates the specific DNA-binding as shown by a decrease in binding affinity characterized by the ZRANK scores. This result was confirmed by the residues Val143Asp, Ala159Pro, Val197Pro, Tyr234Pro and Cys238Pro p53-DNA mutant complexes inducing the loss of important hydrogen bonds, and introduced non-native hydrogen bonds between the two biomolecules. Furthermore, Molecular dynamics (MD) simulations of the experimental mutant forms showed that the structures of the p53 DNA-binding domains were more rigid comparing to the wild-type structure. The MD trajectories of Val134Ala, Arg213Gly and Gly245Ser DNA-binding domain mutants clearly revealed a loss of the flexibility and stability by the structures. This might affect the structural conformation and interfere with the interaction to DNA. Understanding the effects of mutations associated with cancer at a molecular level will be helpful in designing new therapeutics for cancer diseases. === M
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