Calcium-dependent interaction of S100B with the C-terminal domain of the tumor suppressor p53

Irt vitro, the S100B protein interacts with baculovirus recombinant p53 pro tein and protects p53 from thermal denaturation, This effect is isoform-spe cific and is not observed with S100A1, S100A6, or calmodulin, Using truncat ed p53 proteins in the N-terminal (p53(1-320)) and C-terminal (p53(73-393)) domains, we localized the S100B-binding region to the C-terminal region of p53, We have confirmed a calcium-dependent interaction of the S100B with a synthetic peptide corresponding to the C-terminal region of p53 (residues 319-393 in human p53) using plasmon resonance experiments on a BIAcore syst em. In the presence of calcium, the equilibrium affinity of the S100B for t he C-terminal region of p53 immobilized on the sensor chip was 24 +/- 10 nM . To narrow down the region within p53 involved in S100B binding, two synth etic peptides, O1(357-381) (residues 357-381 in mouse p53) and YF-O2(320-34 6) (residues 320-346 in mouse p53), covering the C-terminal region of p53 w ere compared for their interaction with purified S100B, Only YF-O2 peptide interacts with S100B with high affinity. The YF-O2 motif is a critical dete rminant for the thermostability of p53 and also corresponds to a domain res ponsible for cytoplasmic sequestration of p53, Our results may explain the rescue of nuclear wild type p53 activities by S100B in fibroblast cell line s expressing the temperature-sensitive p53val135 mutant at the nonpermissiv e temperature.