Structural changes in the C-terminus of Ca2+-bound rat S100B (beta beta) upon binding to a peptide derived from the C-terminal regulatory domain of p53.
S100B(beta beta) is a dimeric Ca2+-binding protein that interacts with p53, inhibits its phosphorylation by protein kinase C (PKC) and promotes disassembly of the p53 tetramer. Likewise, a 22 residue peptide derived from the C-terminal regulatory domain of p53 has been shown to interact with S100B(beta beta) in a Ca2+-dependent manner and inhibits its phosphorylation by PKC. Hence, structural studies of Ca2+-loaded S100B(beta beta) bound to the p53 peptide were initiated to characterize this interaction. Analysis of nuclear Overhauser effect (NOE) correlations, amide proton exchange rates, 3J(NH-H alpha) coupling constants, and chemical shift index data show that, like apo- and Ca2+-bound S100B(beta beta), S100B remains a dimer in the p53 peptide complex, and each subunit has four helices (helix 1, Glu2-Arg20; helix 2, Lys29-Asn38; helix 3, Gln50-Asp61; helix 4, Phe70-Phe87), four loops (loop 1, Glu21-His25; loop 2, Glu39-Glu49; loop 3, Glu62-Gly66; loop 4, Phe88-Glu91), and two beta-strands (beta-strand 1, Lys26-Lys28; beta-strand 2, Glu67-Asp69), which forms a short antiparallel beta-sheet. However, in the presence of the p53 peptide helix 4 is longer by five residues than in apo- or Ca2+-bound S100B(beta beta). Furthermore, the amide proton exchange rates in helix 3 (K55, V56, E58, T59, L60, D61) are significantly slower than those of Ca2+-bound S100B(beta beta). Together, these observations plus intermolecular NOE correlations between the p53 peptide and S100B(beta beta) support the notion that the p53 peptide binds in a region of S100B(beta beta), which includes residues in helix 2, helix 3, loop 2, and the C-terminal loop, and that binding of the p53 peptide interacts with and induces the extension of helix 4.
Rustandi
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RR
Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore 21201, USA.
Baldisseri
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DM
Drohat
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AC
Weber
D J
DJ
D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009414:Nerve Growth Factors / Q000737:chemistry* / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats; D064568:S100 Calcium Binding Protein beta Subunit; D009418:S100 Proteins; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry / Q000378:metabolism*
D002135:Calcium-Binding Proteins; D009414:Nerve Growth Factors; D010446:Peptide Fragments; D064568:S100 Calcium Binding Protein beta Subunit; D009418:S100 Proteins; C579158:S100b protein, rat; D016159:Tumor Suppressor Protein p53