Duraisingh Manoj T, Maier Alexander G, Triglia Tony, Cowman Alan F
The Walter and Eliza Hall Institute of Medical Research, Melbourne 3050, Australia.
Proc Natl Acad Sci U S A. 2003 Apr 15;100(8):4796-801. doi: 10.1073/pnas.0730883100. Epub 2003 Apr 2.
The Plasmodium falciparum erythrocyte-binding antigen 175 (EBA-175) is a ligand for merozoite invasion into human erythrocytes that binds to glycophorin A in a sialic acid-dependent manner. P. falciparum strain W2mef depends on sialic acid for invasion of erythrocytes, whereas 3D7 is sialic acid-independent. We generated parasites that lack expression or express truncated forms of EBA-175 in W2mef and 3D7. Lack of EBA-175 expression in W2mef parasites was associated with a switch to sialic acid-independent invasion. 3D7 parasites lacking expression of EBA-175 showed no alteration in their ability to utilize sialic acid-independent pathways. Strikingly, both W2mef and 3D7 parasites lacking EBA-175 expression invaded chymotrypsin-treated erythrocytes inefficiently compared with the parental lines. This loss of function suggests that the EBA-175/glycophorin A ligand-receptor interaction is the major chymotrypsin-resistant invasion pathway. Parasite lines with truncated EBA-175 had invasion phenotypes equivalent to parasites lacking expression of EBA-175. The EBA-175 ligand is functional in erythrocyte invasion by merozoites that utilize either sialic acid-dependent or -independent invasion pathways. This finding suggests a model where a minimal affinity supplied by multiple ligand-receptor interactions is required for successful invasion and has implications for EBA-175 as a malaria vaccine candidate.
恶性疟原虫红细胞结合抗原175(EBA-175)是裂殖子侵入人红细胞的一种配体,它以唾液酸依赖的方式与血型糖蛋白A结合。恶性疟原虫W2mef株侵入红细胞依赖唾液酸,而3D7株则不依赖唾液酸。我们构建了在W2mef和3D7中缺乏EBA-175表达或表达截短形式EBA-175的疟原虫。W2mef疟原虫中EBA-175表达的缺失与向不依赖唾液酸侵入的转变有关。缺乏EBA-175表达的3D7疟原虫在利用不依赖唾液酸途径的能力上没有改变。令人惊讶的是,与亲代株相比,缺乏EBA-175表达的W2mef和3D7疟原虫侵入经胰凝乳蛋白酶处理的红细胞的效率都很低。这种功能丧失表明EBA-175/血型糖蛋白A配体-受体相互作用是主要的抗胰凝乳蛋白酶侵入途径。具有截短EBA-175的疟原虫株的侵入表型与缺乏EBA-175表达的疟原虫相同。EBA-175配体在利用依赖或不依赖唾液酸侵入途径的裂殖子侵入红细胞过程中发挥作用。这一发现提示了一个模型,即成功侵入需要多种配体-受体相互作用提供的最小亲和力,这对EBA-175作为疟疾疫苗候选物具有重要意义。