Structural and ITC Characterization of Peptide‐Protein Binding: Thermodynamic Consequences of Cyclization Constraints, a Case Study on Vascular Endothelial Growth Factor Ligands

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Gaucher, Jean‐françois | Reille-Seroussi, Marie | Broussy, Sylvain

Edité par CCSD ; Wiley-VCH Verlag -

International audience. Abstract: Macrocyclization constraints are widely used in the design of protein ligands to stabilize their bioactive con- formation and increase their affinities. However, the resulting changes in binding entropy can be puzzling and uncorrelated to affinity gains. Here, the thermodynamic (Isothermal Titration Calorimetry) and structural (X-ray, NMR and CD) analysis of a complete series of lactam-bridged peptide ligands of the vascular endothelial growth factor, and their unconstrained analogs are reported. It is shown that differ- ences in thermodynamics arise mainly from the foldingIntroductionPeptides have gained increased interest as pharmaceuticals. They share many strengths, such as high target selectivity, good efficiency, safety, and tolerability. However, a short plasma half- life, chemical and physical instabilities and low membrane permeability are weaknesses that must be overcome for therapeutic use. Among the possible strategies, a common approach is to constrain peptides, which can reduce suscepti- bility to proteolysis, stabilize their bioactive form and improve both affinity and specificity. However, attempting to correlate constraints to binding thermodynamics is puzzling, if not impossible. While a gain in binding affinity is often observed, inconsistencies in change of entropy and enthalpy upon bind-energy of the peptide upon binding. The systematic reduc- tion in conformational entropy penalty due to helix pre- organization can be counterbalanced by an unfavorable vibrational entropy change if the constraints are too rigid. The gain in configurational entropy partially escapes the enthalpy/entropy compensation and leads to an improve- ment in affinity. The precision of the analytical ITC method makes this study a possible benchmark for constrained peptides optimization.

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