Pancake S J, Holt G D, Mellouk S, Hoffman S L
Malaria Program, Naval Medical Research Institute, Bethesda, Maryland 20889-5055.
J Cell Biol. 1992 Jun;117(6):1351-7. doi: 10.1083/jcb.117.6.1351.
Circumsporozoite (CS) proteins, which densely coat malaria (Plasmodia) sporozoites, contain an amino acid sequence that is homologous to segments in other proteins which bind specifically to sulfated glycoconjugates. The presence of this homology suggests that sporozoites and CS proteins may also bind sulfated glycoconjugates. To test this hypothesis, recombinant P. yoelii CS protein was examined for binding to sulfated glycoconjugate-Sepharoses. CS protein bound avidly to heparin-, fucoidan-, and dextran sulfate-Sepharose, but bound comparatively poorly to chondroitin sulfate A- or C-Sepharose. CS protein also bound with significantly lower affinity to a heparan sulfate biosynthesis-deficient mutant cell line compared with the wild-type line, consistent with the possibility that the protein also binds to sulfated glycoconjugates on the surfaces of cells. This possibility is consistent with the observation that CS protein binding to hepatocytes, cells invaded by sporozoites during the primary stage of malaria infection, was inhibited by fucoidan, pentosan polysulfate, and heparin. The effects of sulfated glycoconjugates on sporozoite infectivity were also determined. P. berghei sporozoites bound specifically to sulfatide (galactosyl[3-sulfate]beta 1-1ceramide), but not to comparable levels of cholesterol-3-sulfate, or several examples of neutral glycosphingolipids, gangliosides, or phospholipids. Sporozoite invasion into hepatocytes was inhibited by fucoidan, heparin, and dextran sulfate, paralleling the observed binding of CS protein to the corresponding Sepharose derivatives. These sulfated glycoconjugates blocked invasion by inhibiting an event occurring within 3 h of combining sporozoites and hepatocytes. Sporozoite infectivity in mice was significantly inhibited by dextran sulfate 500,000 and fucoidan. Taken together, these data indicate that CS proteins bind selectively to certain sulfated glycoconjugates, that sporozoite infectivity can be inhibited by such compounds, and that invasion of host hepatocytes by sporozoites may involve interactions with these types of compounds.
环子孢子（CS）蛋白紧密包裹着疟原虫的子孢子，其氨基酸序列与其他能特异性结合硫酸化糖缀合物的蛋白质片段具有同源性。这种同源性的存在表明子孢子和CS蛋白可能也能结合硫酸化糖缀合物。为验证这一假说，研究人员检测了重组约氏疟原虫CS蛋白与硫酸化糖缀合物-琼脂糖凝胶的结合情况。CS蛋白能与肝素、岩藻依聚糖和硫酸葡聚糖-琼脂糖凝胶紧密结合，但与硫酸软骨素A或C-琼脂糖凝胶的结合相对较弱。与野生型细胞系相比，CS蛋白与硫酸乙酰肝素生物合成缺陷型突变细胞系的结合亲和力也显著降低，这与该蛋白也能结合细胞表面硫酸化糖缀合物的可能性相符。这一可能性与以下观察结果一致：在疟疾感染初期，子孢子侵入的肝细胞表面，CS蛋白的结合会受到岩藻依聚糖、聚戊糖多硫酸盐和肝素的抑制。研究人员还确定了硫酸化糖缀合物对子孢子感染性的影响。伯氏疟原虫子孢子能特异性结合硫苷脂（半乳糖基[3-硫酸酯]β1-1神经酰胺），但对胆固醇-3-硫酸酯以及几种中性糖鞘脂、神经节苷脂或磷脂的结合水平相当。岩藻依聚糖、肝素和硫酸葡聚糖可抑制子孢子侵入肝细胞，这与观察到的CS蛋白与相应琼脂糖衍生物的结合情况相似。这些硫酸化糖缀合物通过抑制子孢子与肝细胞结合后3小时内发生的一个事件来阻断侵入。硫酸葡聚糖500,000和岩藻依聚糖能显著抑制小鼠体内子孢子的感染性。综上所述，这些数据表明CS蛋白能选择性结合某些硫酸化糖缀合物，此类化合物可抑制子孢子的感染性，且子孢子侵入宿主肝细胞可能涉及与这些化合物的相互作用。
