The DNA binding activity of wild type p53 is modulated by blocking its various antigenic epitopes

Interaction of wild type p53 with specific DNA target sequences, which is dictated by several structural domains, can be modified by blocking the different antigenic epitopes of the protein. Comparison of p53 protein expressed by recombinant bacteria (wtp53-Bac) to that produced in an eukaryotic system by a vaccinia expression vector (wtp53-Vac), indicated that only the later exhibited spontaneous DNA-binding activity. Furthermore, DNA-binding patterns of these wild type p53 proteins were affected differently by their interactions with monoclonal anti-p53 antibodies recognizing individual antigenic epitopes of the molecule. While the vaccinia derived p53 that spontaneously bound DNA is supershifted by the N'-terminal specific antibodies PAb-248, the bacterial derived p53 protein that retains this antigenic epitope but does not bind DNA spontaneously, is not affected. The C'-terminal specific PAb-421 antibodies accelerated binding of the bacterial p53 protein and modified the pattern of the interaction of the vaccinia derived p53 DNA. DNA-binding patterns generated by PAb-421 and PAb-248, suggest that either interaction of wild type p53 is dependent on modification of the p53 protein or that it interacts with cellular factors which their activity can be mimicked by PAb-421. Saturation of both types of wild type p53 with several anti-p53 monoclonal antibodies directed against the wild type p53 specific epitope that maps to the N'-terminal border of the DNA-binding region, blocked specific DNA-binding. The fact that most p53 mutants have lost the wild type p53 conformation specific epitope coupled with the observation that blocking of this site by binding specific antibodies, prevents the interaction of wild type p53 with DNA, suggests that maintaining the correct structural conformation of this site is central for DNA-binding activity. The wild type specific epitope which maps to the N'-terminal border of the DNA-binding region is neighboring the first beta-strand detected by the recent crystallographic analysis.