Mechanism and functional implications of the heme-induced binding promiscuity of IgE.
A fraction of antibodies from healthy immune repertoires binds to heme and acquires the ability to recognize multiple antigens. The mechanism and functional consequences of heme-mediated antigen binding promiscuity (polyreactivity) are not understood. Here, we used SPE7, a mouse monoclonal IgE specific for dinitrophenyl that has been thoroughly characterized at the molecular level, as a model antibody to elucidate the mechanism and functional consequences of heme-mediated polyreactivity. We first demonstrate that exposure of SPE7 to heme results in a substantial increase in its antigen binding polyreactivity. Comparison of the binding kinetics and thermodynamics of interaction of native and heme-bound SPE7 indicates that the binding of heme to SPE7 confers binding affinities in the low nanomolar range toward several antigens but has no influence on the mechanism of recognition of dinitrophenyl. In vitro cellular assays further demonstrate that heme-bound SPE7 does not promote the degranulation of basophils in the presence of new target antigens, while degranulation is observed in the presence of dinitrophenyl. Molecular docking and fluorescence spectroscopy revealed binding of heme to the variable region of SPE7 at a distance from the conventional binding site for dinitrophenyl, explaining the extension of binding polyreactivity without abrogation of the interaction with its cognate antigen. In addition, our data suggest that heme, when bound to IgE, is solvent-exposed and may serve as an interfacial cofactor mediating binding to diverse proteins. This study contributes to the understanding of the mechanisms of heme-induced antibody polyreactivity. It also paves the way toward the delineation of the functional impact of polyreactivity and cross-reactivity of IgE.
†Institute of Microbiology, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria.
Maya
M
Hadzhieva
†Institute of Microbiology, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria.
Tchavdar L
TL
Vassilev
‡Sorbonne Universités, UPMC Univ Paris 06, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.|§INSERM, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.|∥Université Paris Descartes, Sorbonne Paris Cité, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.
Lubka T
LT
Roumenina
‡Sorbonne Universités, UPMC Univ Paris 06, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.|§INSERM, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.|∥Université Paris Descartes, Sorbonne Paris Cité, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.
Jagadeesh
J
Bayry
‡Sorbonne Universités, UPMC Univ Paris 06, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.|§INSERM, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.|∥Université Paris Descartes, Sorbonne Paris Cité, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.
Srinivas V
SV
Kaveri
‡Sorbonne Universités, UPMC Univ Paris 06, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.|§INSERM, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.|∥Université Paris Descartes, Sorbonne Paris Cité, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.
Sébastien
S
Lacroix-Desmazes
‡Sorbonne Universités, UPMC Univ Paris 06, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.|§INSERM, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.|∥Université Paris Descartes, Sorbonne Paris Cité, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006 Paris, France.
Jordan D
JD
Dimitrov
D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000378:metabolism*; D000915:Antibody Affinity; D000918:Antibody Specificity; D001491:Basophils / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D001666:Binding Sites, Antibody; D015550:Cell Degranulation / Q000187:drug effects; D002460:Cell Line; D003429:Cross Reactions; D004136:Dinitrobenzenes / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D006418:Heme / Q000737:chemistry / Q000378:metabolism*; D006427:Hemin / Q000737:chemistry / Q000378:metabolism; D007073:Immunoglobulin E / Q000737:chemistry / Q000378:metabolism*; D007202:Indicators and Reagents / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D051381:Rats; D013050:Spectrometry, Fluorescence
D000911:Antibodies, Monoclonal; D004136:Dinitrobenzenes; D007202:Indicators and Reagents; D007073:Immunoglobulin E; D006418:Heme; D006427:Hemin