Interaction of epitope-related and -unrelated peptides with anti-p24 (HIV-1) monoclonal antibody CB4-1 and its Fab fragment

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Item Type:	Article
Title:	Interaction of epitope-related and -unrelated peptides with anti-p24 (HIV-1) monoclonal antibody CB4-1 and its Fab fragment
Creators Name:	Welfle, K., Misselwitz, R., Hoehne, W. and Welfle, H.
Abstract:	The binding of four epitope-related peptides and three library-derived, epitope-unrelated peptides of different lengths (10-14 amino acids) and sequence by anti-p24 (HIV-1) monoclonal antibody CB4-1 and its Fab fragment was studied by isothermal titration calorimetry. The binding constants KA at 25°C vary between 5.1 × 107 M-1 for the strongest and 1.4 × 105 M-1 for the weakest binder. For each of the peptides complex formation is enthalpicaily driven and connected with unfavorable entropic contributions; however, the ratio of enthalpy and entropy contributions to ΔG0 differs markedly for the individual peptides. A plot of -ΔH0 vs -TΔS0 shows a linear correlation of the data for a wide variety of experimental conditions as expected for a process with ΔCp much larger than ΔS0. The dissimilarity of ΔCp and AS0 also explains why ΔH0 and TΔS0 show similar temperature dependences resulting in relatively small changes of ΔG0 with temperature. The heat capacity changes ΔCp upon antibody-peptide complex formation determined for three selected peptides vary only in a small range, indicating basic thermodynamic similarity despite different key residues interacting in the complexes. Furthermore, the comparison of van't Hoff and calorimetric enthaipies point to a non-two-state binding mechanism. Protonation effects were excluded by measurements in buffers of different ionization enthaipies. Differences in the solution conformation of the peptides as demonstrated by circular dichroic measurements do not explain different binding affinities of the peptides; specifically a high helix content in solution is not essential for high binding affinity despite the helical epitope conformation in the crystal structure of p24.
Keywords:	Binding Constant, Binding Specificity, Circular Dichroism, Isothermal Titration Calorimetry, Animals
Source:	Journal of Molecular Recognition
ISSN:	0952-3499
Publisher:	John Wiley & Sons
Volume:	16
Number:	1
Page Range:	54-62
Date:	1 January 2003
Official Publication:	https://doi.org/10.1002/jmr.607
PubMed:	View item in PubMed

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