Sharon N
FEBS Lett. 1987 Jun 15;217(2):145-57. doi: 10.1016/0014-5793(87)80654-3.
Numerous bacterial strains produce surface lectins, commonly in the form of fimbriae that are filamentous assemblies of protein subunits. Among the best characterized of these are the type 1 (mannose specific) fimbrial lectins of Escherichia coli that consist almost exclusively of one class of subunit with a molecular mass of 17 kDa. They possess an extended combining site corresponding to a trisaccharide and preferentially bind carbohydrate units of oligomannose or hybrid type. Type 1 fimbriae also possess a hydrophobic region close to the carbohydrate-binding site, since aromatic alpha-mannosides inhibit strongly (up to 1000-times more than methyl alpha-mannoside) the agglutination of yeasts by the bacteria and the adherence of the latter to pig ileal epithelial cells. The combining sites of type 1 fimbriae of the salmonellae and of other enteric bacteria are different from those of E. coli in that they are smaller and do not possess a hydrophobic region. The various bacterial surface lectins appear to function primarily in the initiation of infection by mediating bacterial adherence to epithelial cells, e.g. in the urinary and gastrointestinal tracts. The mannose specific lectins also act as recognition molecules in lectinophagocytosis (i.e. phagocytosis of the bacteria in the absence of opsonins) by mouse, rat and human peritoneal macrophages, and human polymorphonuclear leukocytes. Affinity chromatography of membrane lysates from human polymorphonuclear leukocytes on immobilized type 1 fimbrial lectin, using methyl alpha-mannoside as eluent, showed that glycoproteins with apparent molecular masses of 70-80, 100 and 150 kDa act as receptors for the bacteria. Inhibition experiments with monoclonal antibodies suggest that the glycoprotein bands of 100 and 150 kDa may be identical with the alpha and beta subunits of leukocyte complement receptors and adhesion glycoproteins involved in complement-mediated opsonophagocytosis. The systems described serve as a fine illustration for the biological role of lectin-carbohydrate interactions. Further studies of these systems will lead to a deeper understanding of the molecular basis of infectious diseases, and perhaps also to new approaches for their prevention.
许多细菌菌株会产生表面凝集素，通常以菌毛的形式存在，菌毛是蛋白质亚基的丝状聚合体。其中研究得最为透彻的是大肠杆菌的1型（甘露糖特异性）菌毛凝集素，它几乎完全由一类分子量为17 kDa的亚基组成。它们具有一个与三糖相对应的延伸结合位点，优先结合低聚甘露糖或杂合型的碳水化合物单元。1型菌毛在靠近碳水化合物结合位点处还具有一个疏水区域，因为芳香族α-甘露糖苷强烈抑制（比甲基α-甘露糖苷强1000倍）细菌对酵母的凝集作用以及细菌对猪回肠上皮细胞的黏附。沙门氏菌和其他肠道细菌的1型菌毛的结合位点与大肠杆菌的不同，它们较小且不具有疏水区域。各种细菌表面凝集素似乎主要通过介导细菌与上皮细胞的黏附来启动感染，例如在泌尿道和胃肠道中。甘露糖特异性凝集素在小鼠、大鼠和人类腹腔巨噬细胞以及人类多形核白细胞的凝集吞噬作用（即在没有调理素的情况下对细菌的吞噬作用）中也充当识别分子。使用甲基α-甘露糖苷作为洗脱剂，对固定化的1型菌毛凝集素上的人类多形核白细胞膜裂解物进行亲和层析，结果表明表观分子量为70 - 80 kDa、100 kDa和150 kDa的糖蛋白可作为细菌的受体。用单克隆抗体进行的抑制实验表明，100 kDa和150 kDa的糖蛋白条带可能与白细胞补体受体的α和β亚基以及参与补体介导的调理吞噬作用的黏附糖蛋白相同。所描述的这些系统很好地说明了凝集素 - 碳水化合物相互作用的生物学作用。对这些系统的进一步研究将有助于更深入地理解传染病的分子基础，也许还能为其预防带来新方法。
