Influence of magnesium ion on the binding of p53 DNA-binding domain to DNA-response elements

Site-specific recognition and DNA-binding activity of p53 are crucial for its tumour suppressor function. Previous reports have shown that metal ions can affect the specific recognition and DNA-binding activity of p53DBD. Here we firstly report that magnesium ion can bind to the protein and influence its DNA-binding activity. To elucidate the nature and the effect of metal ions in the reaction chemistry, we utilized endogenous tryptophan fluorescence to quantitate the interaction between p53DBD and metal ions. The K(a) value for the binding of Mg(2+) to the protein is 1.88 x 10(3) M(-1). Analysis of the CD data clearly suggested that the binding of magnesium ion induced a subtle conformational change rather than a radical modification of the overall protein architecture. Based on the results of electrophoretic mobility shift assays and fluorescence experiments, we concluded that the binding of Mg(2+) significantly stimulated the binding of the protein to DNA in a sequence-independent manner, which differed from that of zinc ions in a sequence-specific manner. Based on these results and the fact that Mg(2+) exists at relatively high concentration in the cell, we propose that Mg(2+) is one of potential factors to affect or regulate the transactivation of p53.