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Analysis of human CD4-antibody interaction using the BIAcore system
F Velge-Roussel1, P Breton, F Lescure
1CJF INSERM 93-09 Immunologie des Maladies Infectieuses, Equipe Associée INRA d'Immunologie Parasitaire, UFR des Sciences Pharmaceutiques, Tours, France.
Journal of Immunological Methods
|June 14, 1995
Summary
This study characterizes the binding kinetics of an anti-CD4 antibody (IOT4a) to soluble CD4, crucial for HIV entry. The interaction is enthalpy-driven with a positive entropy contribution, suggesting electrostatic interactions stabilize the complex.
Area of Science:
- Immunology
- Virology
- Biophysics
Background:
- The interaction between the CD4 protein and the HIV gp120 protein is a critical initial step for HIV entry into host cells.
- Certain anti-CD4 antibodies have demonstrated the ability to inhibit this essential interaction.
Purpose of the Study:
- To determine the kinetic and thermodynamic parameters of the interaction between the anti-CD4 antibody IOT4a and immobilized recombinant soluble CD4 (rsCD4).
Main Methods:
- Utilized biosensor studies with a BIAcore instrument to analyze the antibody-antigen interaction.
- Employed non-linear regression analysis of sensorgrams to model the binding kinetics.
- Calculated kinetic and thermodynamic parameters, including association constant (KA), enthalpy change, and entropy change.
Main Results:
- The interaction between IOT4a and rsCD4 exhibited a double exponential time curve.
- An association constant (KA) of 5.2 x 10^7 M^-1 was determined at 25°C.
- Complex formation was exothermic (-4.5 kcal/mol) and entropically favorable (+20 cal/mol·K), indicating an enthalpy-driven process with a significant positive entropy contribution, likely due to electrostatic interactions.
Conclusions:
- The binding kinetics and thermodynamics of IOT4a-rsCD4 interaction were quantitatively characterized.
- The observed thermodynamic profile, particularly the positive entropy contribution, differs from some antigen-antibody models and suggests a role for electrostatic interactions.
- The findings validate the theoretical approach used for analyzing the sensorgrams and provide insights into the molecular basis of antibody-antigen recognition in the context of HIV-CD4 interaction.