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Conformational and thermodynamic properties of peptide binding to the human S100P protein
Author(s) -
Gribenko Alexey V.,
GuzmánCasado Mercedes,
Lopez Maria M.,
Makhatadze George I.
Publication year - 2002
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.0202202
Subject(s) - melittin , isothermal titration calorimetry , chemistry , peptide , dimer , cooperativity , conformational change , biophysics , calmodulin , circular dichroism , crystallography , biochemistry , biology , organic chemistry , enzyme
S100P is a member of the S100 subfamily of calcium‐binding proteins that are believed to be associated with various diseases, and in particular deregulation of S100P expression has been documented for prostate and breast cancer. Previously, we characterized the effects of metal binding on the conformational properties of S100P and proposed that S100P could function as a Ca 2+ conformational switch. In this study we used fluorescence and CD spectroscopies and isothermal titration calorimetry to characterize the target‐recognition properties of S100P using a model peptide, melittin. Based on these experimental data we show that S100P and melittin can interact in a Ca 2+ ‐dependent and ‐independent manner. Ca 2+ ‐independent binding occurs with low affinity ( K d ≈ 0.2 mM), has a stoichiometry of four melittin molecules per S100P dimer and is presumably driven by favorable electrostatic interactions between the acidic protein and the basic peptide. In contrast, Ca 2+ ‐dependent binding of melittin to S100P occurs with high affinity ( K d ≈ 5 μM) has a stoichiometry of two molecules of melittin per S100P dimer, appears to have positive cooperativity, and is driven by hydrophobic interactions. Furthermore, Ca 2+ ‐dependent S100P‐melittin complex formation is accompanied by significant conformational changes: Melittin, otherwise unstructured in solution, adopts a helical conformation upon interaction with Ca 2+ ‐S100P. These results support a model for the Ca 2+ ‐dependent conformational switch in S100P for functional target recognition.