Expression, purification and structural analysis of human IL-18 binding protein: a potent therapeutic molecule for allergy.
BACKGROUND
While interleukin-18 (IL-18) plays an important role in the innate and adaptive immune responses, it can also cause severe allergic inflammatory reactions. Thus it is a molecule currently being targeted for therapy. The natural intrinsic inhibitor of IL-18 receptor activation, IL-18 binding protein (IL-18BP), shows a great potential for the treatment of allergy.


METHODS
Expression and purification of recombinant human IL-18BP (rhIL-18BP) were performed using the baculovirus system to develop a therapeutic molecule for the treatment of IL-18-related diseases and to investigate the structural basis of its inhibitory mechanism.


RESULTS
Purified rhIL-18BP potently inhibited the production of interferon-gamma by peripheral blood mononuclear cells in the presence of lipopolysaccharide and by human myelomonocytic KG-1 cells in the presence of IL-18 (IC50 = 0.4 nM). Surface plasmon resonance showed a high affinity (Kd = 0.46 nM) for rhIL-18BP in binding hIL-18. Structural analysis indicated that the stoichiometry between IL-18 and IL-18BP is 1 : 1 in solution and the model structure of the complex suggests that the key residues on IL-18 (L5, K53, S55) and the estimated key residues on IL-18BP (F93,Y97, F104) could have interactions. The structural mechanism of IL-18BP inhibition might be a competition for Site 2 on rIL-18 so that IL-18BP can prevent IL-18 receptor alpha from binding to Site 2 and inhibit IL-18 receptor activation.


CONCLUSIONS
IL-18BP has unique features with respect to its structure, binding mode and inhibitory mechanism. It is a molecule that has a great potential for the therapy of allergy.
Kimura
Takeshi
T
Department of Pediatrics, Graduate School of Medicine, Gifu University, Gifu, Japan.
Kato
Zenichiro
Z
Ohnishi
Hidenori
H
Tochio
Hidehito
H
Shirakawa
Masahiro
M
Kondo
Naomi
N
D016367:Baculoviridae / Q000235:genetics; D001667:Binding, Competitive; D002478:Cells, Cultured; D015870:Gene Expression; D006801:Humans; D006967:Hypersensitivity / Q000276:immunology* / Q000628:therapy; D007167:Immunotherapy / Q000639:trends; D036341:Intercellular Signaling Peptides and Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D007371:Interferon-gamma / Q000378:metabolism; D020382:Interleukin-18 / Q000276:immunology / Q000378:metabolism*; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000276:immunology; D008213:Lymphocyte Activation / Q000187:drug effects; D008956:Models, Chemical; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D053724:Receptors, Interleukin-18 / Q000737:chemistry / Q000276:immunology; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D020349:Surface Plasmon Resonance
D036341:Intercellular Signaling Peptides and Proteins; D020382:Interleukin-18; D008070:Lipopolysaccharides; D053724:Receptors, Interleukin-18; D011994:Recombinant Proteins; C118370:interleukin-18 binding protein; D007371:Interferon-gamma