Identification of Linear Epitopes in Bacillus anthracis Protective Antigen Bound by Neutralizing Antibodies
Identification of Linear Epitopes in Bacillus anthracis Protective Antigen Bound by Neutralizing Antibodies
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DOI：
10.1074/jbc.m109.022061
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发表时间：
2009-09-11
影响因子：
4.8
通讯作者：
Casadevall, Arturo
中科院分区：
文献类型：
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作者：
Abboud, Nareen;De Jesus, Magdia;Casadevall, Arturo
保护性抗原（PA）是炭疽毒素的结合亚基，是目前炭疽疫苗的主要成分，但PA的精细抗原结构尚不清楚。为了鉴定 PA 的线性中和表位，合成了 145 个覆盖蛋白质整个序列的重叠肽。通过酶联免疫吸附测定，测试了六种单克隆抗体 (mAb) 和来自 PA 特异性小鼠的抗血清对肽的反应性。三个主要的线性免疫显性 B 细胞表位被映射到 PA 蛋白的残基 Leu(156) 至 Ser(170)、Val(196) 至 Ile(210) 以及 Ser(312) 至 Asn(326)。两种具有毒素中和活性的单克隆抗体可识别靠近结构域 1 中弗林蛋白酶裂解位点的两个不同表位。使用分子对接方法对 PA 及其中和单克隆抗体 7.5G 和 19D9 的三维复杂结构进行建模，为相互作用的表位和互补位残基提供模型。对于这两种 mAb，LeTx 中和与干扰弗林蛋白酶裂解有关，但它们的有效性有所不同，具体取决于它们是否与裂解产物的 N 端或 C 端结合。含有这些表位（包括氨基酸 Leu(156)-Ser(170) 和 Val(196)-Ile(210)）的两种肽具有免疫原性，并引发针对 PA 的中和抗体反应。这些结果鉴定了 PA 的第一个线性中和表位，并表明含有表位序列的肽可以引发中和抗体反应，这一发现可用于疫苗设计。
Protective antigen (PA), the binding subunit of anthrax toxin, is the major component in the current anthrax vaccine, but the fine antigenic structure of PA is not well defined. To identify linear neutralizing epitopes of PA, 145 overlapping peptides covering the entire sequence of the protein were synthesized. Six monoclonal antibodies (mAbs) and antisera from mice specific for PA were tested for their reactivity to the peptides by enzyme-linked immunosorbent assays. Three major linear immunodominant B-cell epitopes were mapped to residues Leu(156) to Ser(170), Val(196) to Ile(210), and Ser(312) to Asn(326) of the PA protein. Two mAbs with toxin-neutralizing activity recognized two different epitopes in close proximity to the furin cleavage site in domain 1. The three-dimensional complex structure of PA and its neutralizing mAbs 7.5G and 19D9 were modeled using the molecular docking method providing models for the interacting epitope and paratope residues. For both mAbs, LeTx neutralization was associated with interference with furin cleavage, but they differed in effectiveness depending on whether they bound on the N- or C-terminal aspect of the cleaved products. The two peptides containing these epitopes that include amino acids Leu(156)-Ser(170) and Val(196)-Ile(210) were immunogenic and elicited neutralizing antibody responses to PA. These results identify the first linear neutralizing epitopes of PA and show that peptides containing epitope sequences can elicit neutralizing antibody responses, a finding that could be exploited for vaccine design.