Helix folding upon binding is involved in a number of protein-protein interactions.  Is helix folding a rate limiting step for binding or coil-to-helix transition occurs after encounter complex formation?  We used isothermal titration calorimetry (ITC) and NMR line shape analysis to characterize both the thermodynamics and kinetics of binding of several peptide targets (p53, HDM, TRTK12, melittin) to human S100B protein.  S100B protein belongs to a S100 protein family of Ca2+-binding proteins.  Binding of Ca2+ leads to conformational changes in S100B that exposes target binding interface formed by both hydrophobic and polar residues.  The target peptides have different sequences, differ in length, and have different intrinsic helix propensity.  We find extremely fast association rates that are modulated by electrostatic interactions.  The results are discussed in terms of possible models that account for this fast association rates (e.g. fly casting, conformation sampling, etc).

Helix-coil transition in protein-protein interactions

243rd National Meeting (2012)

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