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HSP70 binding sites in the tumor suppressor protein p53
A M Fourie1, T R Hupp, D P Lane
1R. W. Johnson Pharmaceutical Research Institute, San Diego, California 92121, USA.
Abstract:
Mutations within conserved regions of the tumor suppressor protein, p53, result in oncogenic forms of the protein with altered tertiary structures. In most cases, the mutant p53 proteins are selectively recognized and bound by members of the HSP70 family of molecular chaperones, but the binding site(s) in p53 for these chaperones have not been clearly defined. We have screened a library of overlapping biotinylated peptides, spanning the entire human p53 sequence, for binding to the HSP70 proteins, Hsc70 and DnaK. We show that most of the high affinity binding sites for these proteins map to secondary structure elements, particularly beta-strands, in the hydrophobic core of the central DNA binding domain, where the majority of oncogenic p53 mutations are found. Although peptides corresponding to the C-terminal region of p53 also contain potential binding sites, p53 proteins with C-terminal deletions are capable of binding to Hsc70, indicating that this region is not required for complex formation. We propose that mutations in the p53 protein alter the tertiary structure of the central DNA binding domain, thus exposing high affinity HSP70 binding sites that are cryptic in the wild-type molecule.
Insights
Mutant tumor suppressor p53 proteins bind HSP70 chaperones at sites within the DNA binding domain. These sites become exposed due to structural changes caused by mutations, unlike in wild-type p53.
Area of Science:
- Molecular Biology
- Protein Biochemistry
- Cancer Research
Background:
- Mutations in the tumor suppressor protein p53 can lead to oncogenic forms with altered structures.
- Members of the HSP70 family of molecular chaperones bind to these mutant p53 proteins.
- The specific binding sites of HSP70 chaperones on p53 have not been fully identified.
Purpose of the Study:
- To identify the binding sites of HSP70 proteins (Hsc70 and DnaK) on the human p53 protein.
- To understand the role of p53 structure in chaperone binding.
Main Methods:
- Screening of overlapping biotinylated peptides spanning the human p53 sequence.
- Assessing peptide binding to Hsc70 and DnaK.
Main Results:
- High-affinity HSP70 binding sites on p53 predominantly map to secondary structure elements, specifically beta-strands, within the central DNA binding domain.
- The majority of oncogenic p53 mutations occur in this same region.
- While the C-terminal region of p53 shows potential binding sites, it is not essential for Hsc70 complex formation.
Conclusions:
- Mutations in p53 alter its tertiary structure, exposing previously hidden (cryptic) high-affinity HSP70 binding sites in the DNA binding domain.
- This suggests a mechanism where chaperone binding is mediated by structural changes in mutant p53.