The core epitope of 2F5 was mapped onto the662ELDKWAS668linear sequence of gp41, which is located in the membrane-proximal external region (MPER) of the protein
The core epitope of 2F5 was mapped onto the662ELDKWAS668linear sequence of gp41, which is located in the membrane-proximal external region (MPER) of the protein. binding of these bNAbs and their epitopes. We used isothermal titration calorimetry to characterize thermodynamically the relationships between bNAb 2F5 (in both the IgG and Fab forms) and its practical and core epitope peptides. We found that these relationships are enthalpically driven and opposed by a negative entropy switch. The highest affinity was found for 2F5 IgG for its practical epitope, indicating that additional relationships including residues flanking the core epitope contribute strongly to higher affinity. In addition, the strong influence of the Fc region within the binding affinity suggests long-range allosteric effects within IgG. Our results provide useful info for developing fresh therapeutics against HIV-1 and, inside a broader H-Ala-Ala-Tyr-OH scope, contribute to a better understanding of antigen-antibody acknowledgement. == Intro == Since 1983, when HIV was found to become the causal agent of AIDS, great efforts have been made to design an effective vaccine to contain the disease. Despite these attempts and actually after encouraging results from the RV144 vaccine medical trial (1), developing an HIV vaccine is still a daunting challenge. However, the field of HIV vaccine study offers experimented a resurgence with the recognition of antibodies that neutralize most circulating HIV-1 strains. Eliciting broadly neutralizing antibodies (bNAbs)2provides a base for active and passive immunization strategies to prevent HIV illness (2). These antibodies can protect against illness and suppress founded HIV illness in animal models. The finding that these antibodies develop inside a portion of infected individuals supports the idea that new approaches to vaccination might be developed by adapting the natural immune strategies or by structure-based design of immunogens (3). One of these bNAbs, 2F5, was found out in a first generation of bNAbs against HIV-1 and has been extensively analyzed. bNAb 2F5 offers strong neutralizing activity against a broad range of HIV-1 main isolates (46). The core epitope of 2F5 was mapped onto the662ELDKWAS668linear sequence of gp41, which is located H-Ala-Ala-Tyr-OH in the membrane-proximal external region (MPER) of the protein. A functional epitope including those residues whose substitution modifies the affinity for the related antibody was later on extended to the sequence656NEQELLELDKWASLWN671(7). The atomic relationships of the complex between the core epitope and antibody 2F5 have been described in detail (810). An additional complexity of the 2F5 epitope has been suggested, including additional gp41 areas (11) and an influence of the proximal lipid bilayer (12,13), which strongly affects its immunogenicity (14). Understanding the connection of this antibody with its epitope requires not only a detailed knowledge of the structure Rabbit Polyclonal to Syntaxin 1A (phospho-Ser14) but also knowing the physicochemical characteristics of the antigen (Ag)-antibody complex described from the kinetic rate constants, equilibrium constants, and thermodynamics of binding. Moreover, affinity and specificity are two of the most fundamental ideas of relevance to the molecular immunologist interested in understanding and characterizing Ag-Ab relationships. These concepts can be usefully defined in more than one way (15), but for some purposes, both terms can be specified exactly and quantitatively by reference H-Ala-Ala-Tyr-OH to thermodynamics. However, very few data have been reported to day about the thermodynamics of binding of the connection between bNAb 2F5 and its related epitope peptide, and they account only for the Fab portion (16). In this study, we have characterized thermodynamically the binding of bNAb 2F5 to peptides related to both the core and practical epitopes by isothermal titration calorimetry (ITC). This technique is the only one capable of measuring not only the binding affinity but also its stoichiometry and the magnitude of the two thermodynamic terms that define the binding affinity: the enthalpy (H) and entropy (S) changes. In contrast, several authors possess reported that both variable (V) and constant (C) Ig areas contribute to the binding affinity and specificity of antibodies (11,1723). Most of these studies possess focused on affinity variations between unique Ig isotypes. For instance, the IgG isotype offers been shown to impact the Ag-binding and HIV-neutralizing activity of monoclonal (24) and polyclonal (25) antibodies. Furthermore, 2F5 IgA2 and IgG1 display significantly different epitope specificity, antibody affinity, and practical activities (11). It remains unclear whether allosteric influence between C and V areas is limited to the Fab website or extends further to the hinge and Fc regions of Ig. This may be clarified by a comparative analysis of epitope acknowledgement between IgG and its Fab fragment. However, very few comparative thermodynamic studies of this type by ITC have been reported. This information would help to elucidate whether the flexibility of.