Henderson Kylie A, Streltsov Victor A, Coley Andrew M, Dolezal Olan, Hudson Peter J, Batchelor Adrian H, Gupta Aditi, Bai Tao, Murphy Vincent J, Anders Robin F, Foley Michael, Nuttall Stewart D
CSIRO Molecular and Health Technologies, 343 Royal Parade, Parkville 3052, Australia.
Structure. 2007 Nov;15(11):1452-66. doi: 10.1016/j.str.2007.09.011.
Apical membrane antigen 1 (AMA1) is essential for invasion of erythrocytes and hepatocytes by Plasmodium parasites and is a leading malarial vaccine candidate. Although conventional antibodies to AMA1 can prevent such invasion, extensive polymorphisms within surface-exposed loops may limit the ability of these AMA1-induced antibodies to protect against all parasite genotypes. Using an AMA1-specific IgNAR single-variable-domain antibody, we performed targeted mutagenesis and selection against AMA1 from three P. falciparum strains. We present cocrystal structures of two antibody-AMA1 complexes which reveal extended IgNAR CDR3 loops penetrating deep into a hydrophobic cleft on the antigen surface and contacting residues conserved across parasite species. Comparison of a series of affinity-enhancing mutations allowed dissection of their relative contributions to binding kinetics and correlation with inhibition of erythrocyte invasion. These findings provide insights into mechanisms of single-domain antibody binding, and may enable design of reagents targeting otherwise cryptic epitopes in pathogen antigens.
顶端膜抗原1（AMA1）对于疟原虫侵入红细胞和肝细胞至关重要，是一种主要的疟疾疫苗候选物。尽管针对AMA1的传统抗体可以阻止这种侵入，但表面暴露环内广泛的多态性可能会限制这些AMA1诱导的抗体抵御所有寄生虫基因型的能力。我们使用一种AMA1特异性IgNAR单可变域抗体，对来自三种恶性疟原虫菌株的AMA1进行了靶向诱变和筛选。我们展示了两种抗体-AMA1复合物的共晶体结构，这些结构揭示了延伸的IgNAR互补决定区3（CDR3）环深入穿透抗原表面的疏水裂缝，并与跨寄生虫物种保守的残基接触。对一系列亲和力增强突变的比较，使得能够剖析它们对结合动力学的相对贡献以及与抑制红细胞侵入的相关性。这些发现为单域抗体结合机制提供了见解，并可能有助于设计针对病原体抗原中其他隐蔽表位的试剂。
