Frisardi M, Ghosh S K, Field J, Van Dellen K, Rogers R, Robbins P, Samuelson J
Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
Infect Immun. 2000 Jul;68(7):4217-24. doi: 10.1128/IAI.68.7.4217-4224.2000.
The infectious stage of amebae is the chitin-walled cyst, which is resistant to stomach acids. In this study an extraordinarily abundant, encystation-specific glycoprotein (Jacob) was identified on two-dimensional protein gels of cyst walls purified from Entamoeba invadens. Jacob, which was acidic and had an apparent molecular mass of approximately 100 kDa, contained sugars that bound to concanavalin A and ricin. The jacob gene encoded a 45-kDa protein with a ladder-like series of five Cys-rich domains. These Cys-rich domains were reminiscent of but not homologous to the Cys-rich chitin-binding domains of insect chitinases and peritrophic matrix proteins that surround the food bolus in the insect gut. Jacob bound purified chitin and chitin remaining in sodium dodecyl sulfate-treated cyst walls. Conversely, the E. histolytica plasma membrane Gal/GalNAc lectin bound sugars of intact cyst walls and purified Jacob. In the presence of galactose, E. invadens formed wall-less cysts, which were quadranucleate and contained Jacob and chitinase (another encystation-specific protein) in secretory vesicles. A galactose lectin was found to be present on the surface of wall-less cysts, which phagocytosed bacteria and mucin-coated beads. These results suggest that the E. invadens cyst wall forms when the plasma membrane galactose lectin binds sugars on Jacob, which in turn binds chitin via its five chitin-binding domains.
阿米巴原虫的感染阶段是有几丁质壁的包囊，它对胃酸具有抗性。在本研究中，从侵袭内阿米巴中纯化出的包囊壁二维蛋白质凝胶上鉴定出一种异常丰富的、包囊化特异性糖蛋白（雅各布蛋白）。雅各布蛋白呈酸性，表观分子量约为100 kDa，含有与伴刀豆球蛋白A和蓖麻毒素结合的糖类。雅各布基因编码一种45 kDa的蛋白质，具有一系列呈阶梯状的五个富含半胱氨酸的结构域。这些富含半胱氨酸的结构域让人联想到昆虫几丁质酶和昆虫肠道中包裹食物团的围食膜蛋白的富含半胱氨酸的几丁质结合结构域，但并不与之同源。雅各布蛋白能结合纯化的几丁质以及残留在经十二烷基硫酸钠处理的包囊壁中的几丁质。相反，溶组织内阿米巴质膜半乳糖/ N - 乙酰半乳糖胺凝集素能结合完整包囊壁和纯化的雅各布蛋白的糖类。在有半乳糖存在的情况下，侵袭内阿米巴形成无壁包囊，这些包囊四核化，且分泌小泡中含有雅各布蛋白和几丁质酶（另一种包囊化特异性蛋白）。发现无壁包囊表面存在一种半乳糖凝集素，它能吞噬细菌和黏液包被的珠子。这些结果表明，当质膜半乳糖凝集素结合雅各布蛋白上的糖类时，侵袭内阿米巴包囊壁形成，而雅各布蛋白又通过其五个几丁质结合结构域结合几丁质。
