Kuo K W, Chang L S, Lin P M, Leaber R J, Chang C C
Department of Biochemistry, Kaohsiung Medical College, Taiwan.
J Biochem. 1994 Dec;116(6):1227-32. doi: 10.1093/oxfordjournals.jbchem.a124668.
Anti-cobrotoxin antibodies can be separated into precipitin and non-precipitin antibodies. The precipitin antibody possesses the same binding affinity to cobrotoxin as non-precipitin antibody, but the neutralizing capability of the latter is superior to that of the former in blocking cobrotoxin binding to nicotinic acetylcholine receptor (nAChR). After preincubation with antibodies, cobrotoxin completely lost its binding activity to nAChR. The dissociation of cobrotoxin-nAChR complex by the antibodies was low, and 60% of the complex formation appeared to be irreversible. These results indicate that the neutralization of cobrotoxin by the antibody may predominantly involve unbound, receptor-free cobrotoxin. The relationships of neutralization capacity and binding affinity as well as bond strength between cobrotoxin and its antibodies are incongruous. Different local conformational changes of a unique Trp in cobrotoxin on binding with the precipitin and non-precipitin antibodies seem to lead to different accessibility for fluorescence quenchers. Characterization of the binding domains by immunoprecipitation with the antibodies correlated with the quenching results. Thus, the binding topography of cobrotoxin may play an important role over the binding affinity and bond strength in neutralization by cobrotoxin antibody.
抗眼镜蛇毒素抗体可分为沉淀素抗体和非沉淀素抗体。沉淀素抗体与非沉淀素抗体对眼镜蛇毒素具有相同的结合亲和力，但在阻断眼镜蛇毒素与烟碱型乙酰胆碱受体（nAChR）结合方面，后者的中和能力优于前者。与抗体预孵育后，眼镜蛇毒素完全丧失了其与nAChR的结合活性。抗体对眼镜蛇毒素 - nAChR复合物的解离作用较弱，且60%的复合物形成似乎是不可逆的。这些结果表明，抗体对眼镜蛇毒素的中和作用可能主要涉及未结合的、无受体的眼镜蛇毒素。眼镜蛇毒素与其抗体之间的中和能力、结合亲和力以及结合强度之间的关系并不一致。眼镜蛇毒素中一个独特色氨酸在与沉淀素和非沉淀素抗体结合时不同的局部构象变化，似乎导致了荧光猝灭剂有不同的可及性。用抗体进行免疫沉淀对结合结构域的表征与猝灭结果相关。因此，眼镜蛇毒素的结合拓扑结构在眼镜蛇毒素抗体的中和作用中，可能对结合亲和力和结合强度起重要作用。
