title: Thermodynamic analysis of the binding of 2F5 (Fab and immunoglobulin G forms) to its gp41 epitope reveals a strong influence of the immunoglobulin Fc region on affinity.
abstract: Immunotherapies and vaccines based on the induction of broadly neutralizing monoclonal antibodies (bNAbs) have become outstanding strategies against HIV-1. Diverse bNAbs recognizing different regions of the HIV-1 envelope have been identified and extensively studied. However, there is little information about the thermodynamics of binding of these bNAbs and their epitopes. We used isothermal titration calorimetry to characterize thermodynamically the interactions between bNAb2F5 (in both the IgG and Fab forms) and its functional and core epitope peptides. We found that these interactions are enthalpically driven and opposed by a negative entropy change. The highest affinity was found for 2F5 IgG for its functional epitope, indicating that additional interactions involving residues flanking the core epitope contribute strongly to higher affinity. In addition, the strong influence of the Fc region on the binding affinity suggests long-range allosteric effects within IgG. Our results provide useful information for developing new therapeutics against HIV-1 and, in a broader scope, contribute to a better understanding of antigen-antibody recognition.
authors.affiliation: From the Departamento de Química Física e Instituto de Biotecnología, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain.
authors.forename: Sara
authors.initials: S
authors.lastname: Crespillo
authors.forename: Salvador
authors.initials: S
authors.lastname: Casares
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Mateo
authors.forename: Francisco
authors.initials: F
authors.lastname: Conejero-Lara
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D057134:Antibodies, Neutralizing / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D000915:Antibody Affinity / Q000276:immunology; D001667:Binding, Competitive / Q000276:immunology; D002151:Calorimetry / Q000379:methods; D000939:Epitopes / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D015700:HIV Envelope Protein gp41 / Q000276:immunology; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D007141:Immunoglobulin Fc Fragments / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D007074:Immunoglobulin G / Q000276:immunology; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000276:immunology; D013816:Thermodynamics
chemical_list: D000911:Antibodies, Monoclonal; D057134:Antibodies, Neutralizing; D000939:Epitopes; D015700:HIV Envelope Protein gp41; D007140:Immunoglobulin Fab Fragments; D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G
keywords: Antibodies; HIV-1; Isothermal Titration Calorimetry; MPER; Peptides; Thermodynamics; gp41