Inhibition by Flavonoids of Amyloid-like Fibril Formation by Plasmodium falciparum Merozoite Surface Protein 2
Inhibition by Flavonoids of Amyloid-like Fibril Formation by Plasmodium falciparum Merozoite Surface Protein 2
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DOI：
10.1021/bi902197x
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发表时间：
2010-07-20
期刊：
影响因子：
2.9
通讯作者：
Norton, Raymond S.
中科院分区：
文献类型：
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作者：
Chandrashekaran, Indu R.;Adda, Christopher G.;Norton, Raymond S.
裂殖子表面蛋白2(MSP2)是一种糖基磷脂酰肌醇(GPI)锚定蛋白，在恶性疟原虫裂殖子表面大量表达。在巴布亚新几内亚儿童中进行的第二阶段试验结果表明，MSP2是一种很有前途的疟疾疫苗候选者。MSP2本质上是无结构的，在生理条件下形成淀粉样纤维。含有类似于淀粉样蛋白纤维的β-链相互作用的寡聚体可能是恶性疟原虫裂殖子表面纤维涂层的一种成分。由于MSP2在溶液中形成纤维的倾向也有可能阻碍其作为候选疫苗的发展，因此寻找一种特异性抑制纤维形成的抑制剂可能会促进疫苗的开发。在这项研究中，我们测试了三种黄酮类化合物EGCG、黄芩素和白藜芦醇抑制MSP2纤维形成的能力，发现EGCG对MSP2纤维形成有明显的抑制作用，而另外两种黄酮类化合物没有明显的抑制作用。用核磁共振光谱、硫代黄素T荧光分析、电子显微镜等生物物理方法表征了黄酮类化合物对MSP2的抑制作用及其与MSP2的相互作用。EGCG通过阻止MSP2从随机卷曲到淀粉样β-折叠结构的构象转变来稳定可溶低聚物并阻止纤维形成。三种黄酮类化合物的结构比较表明，它们的自氧化倾向与它们的纤维抑制活性之间存在联系；EGCG的活性可以归因于这种黄酮类化合物中存在的邻近羟基和它们形成苯二酮的能力。EGCG抑制原纤维的分子机制似乎很复杂，涉及到非共价结合，然后是蛋白质的共价修饰。虽然添加EGCG似乎是稳定溶液中MSP2的一种有效手段，但MSP2的共价修饰在疫苗配方中很可能是不可接受的。然而，这些MSP2纤维形成的小分子抑制剂将作为机械探针用于研究MSP2的齐聚和纤维组装。
Merozoite surface protein 2 (MSP2) is a glycosylphosphatidylinositol (GPI)-anchored protein expressed abundantly on the surface of Plasmodium falciparum merozoites. The results of a phase 2 trial in Papua New Guinean children showed MSP2 to be a promising malaria vaccine candidate. MSP2 is intrinsically unstructured and forms amyloid-like fibrils under physiological conditions. Oligomers containing beta-strand interactions similar to those in amyloid fibrils may be a component of the fibrillar surface coat on P. falciparum merozoites. As the propensity of MSP2 to form fibrils in solution also has the potential to impede its development as a vaccine candidate, finding an inhibitor that specifically inhibits fibrillogenesis may enhance vaccine development. In this study, we tested the ability of three flavonoids, EGCG, baicalein, and resveratrol, to inhibit MSP2 fibrillogenesis and found marked inhibition with EGCG but not with the other two flavonoids. The inhibitory effect and the interactions of the flavonoids with MSP2 were characterized using NMR spectroscopy, thioflavin T fluorescence assays, electron microscopy, and other biophysical methods. EGCG stabilizes soluble oligomers and blocks fibrillogenesis by preventing the conformational transition of MSP2 from a random coil to an amyloidogenic beta-sheet structure. Structural comparison of the three flavonoids indicates an association between their propensity for autoxidation and their fibril inhibitory activity; the activity of EGCG can be attributed to the vicinal hydroxyl groups present in this flavonoid and their ability to form quinones. The molecular mechanism of fibril inhibition by EGCG appears to be complex and involves noncovalent binding followed by covalent modification of the protein. Although the addition of EGCG appears to be an effective means of stabilizing MSP2 in solution, the covalent modification of MSP2 would most likely not be acceptable in a vaccine formulation. However, these small molecule inhibitors of MSP2 fibril formation will be useful as mechanistic probes in studying oligomerization and fibril assembly of MSP2.