Wu June H, Singh Tanuja, Herp Anthony, Wu Albert M
Department of Microbiology and Immunology, Chang-Gung, University, Kwei-san, Tao-yuan 333, Taiwan.
Biochimie. 2006 Feb;88(2):201-17. doi: 10.1016/j.biochi.2005.07.007. Epub 2005 Aug 18.
Ricin (RCA60) is a potent cytotoxic protein with lectin domains, contained in the seeds of the castor bean Ricinus communis. It is a potential biohazard. To corroborate the biological properties of ricin, it is essential to understand the recognition factors involved in the ricin-glycotope interaction. In previous reports, knowledge of the binding properties of ricin was limited to oligosugars and glycopeptides with different specificities. Here, recognition factors of the lectin domains in ricin were examined by enzyme-linked lectinosorbent (ELLSA) and inhibition assays, using mammalian Gal/GalNAc structural units and corresponding polyvalent forms. Except for blood group GalNAcalpha1-3Gal (A) active and Forssman (GalNAcalpha1-3GalNAc, F) disaccharides, ricin has a broad range of affinity for mammalian disaccharide structural units-Galbeta1-4Glcbeta1-(Lbeta), Galbeta1-4GlcNAc (II), Galbeta1-3GlcNAc (I), Galbeta1-3GalNAcalpha1-(Talpha), Galbeta1-3GalNAcbeta1-(Tbeta), Galalpha1-3Gal (B), Galalpha1-4Gal (E), GalNAcbeta1-3Gal (P), GalNAcalpha1-Ser/Thr (Tn) and GalNAcbeta1-4Gal (S). Among the polyvalent glycotopes tested, ricin reacted best with type II-containing glycoproteins (gps). It also reacted well with several T (Thomsen-Friedenreich), tumor-associated Tn and blood group Sd. (a+)-containing gps. Except for bird nest and Tamm-Horsfall gps (THGP), this lectin reacted weakly or not at all with ABH-blood type and sialylated gps. From the present and previous results, it can be concluded that: (i) the combining sites of these lectin domains should be a shallow-groove type, recognizing Galbeta1-4Glcbeta1- and Galbeta1-3(4)GlcNAcbeta- as the major binding site; (ii) its size may be as large as a tetrasaccharide and most complementary to lacto-N-tetraose (Galbeta1-3GlcNAc beta1-3Galbeta1-4Glc) and lacto-N-neotetraose (Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc); (iii) the polyvalency of glycotopes, in general, enhances binding; (iv) a hydrophobic interaction in the vicinity of the binding site for sugar accommodation, increases the affinity for Galbeta-. This study should assist in understanding the glyco-recognition factors involved in carbohydrate-toxin interactions in biological processes. The effect of the polyvalent P/S glycotopes on ricin binding should be examined. However, this is hampered by the lack of availability of suitable reagents.
蓖麻毒素（RCA60）是一种含有凝集素结构域的强效细胞毒性蛋白，存在于蓖麻籽中。它是一种潜在的生物危害物。为了证实蓖麻毒素的生物学特性，了解蓖麻毒素与糖表位相互作用中涉及的识别因子至关重要。在以往的报道中，蓖麻毒素结合特性的知识仅限于具有不同特异性的寡糖和糖肽。在此，利用哺乳动物的Gal/GalNAc结构单元及其相应的多价形式，通过酶联凝集素吸附法（ELLSA）和抑制试验，对蓖麻毒素中凝集素结构域的识别因子进行了研究。除了血型GalNAcalpha1-3Gal（A）活性和福斯曼（GalNAcalpha1-3GalNAc，F）二糖外，蓖麻毒素对哺乳动物二糖结构单元——Galbeta1-4Glcbeta1-（Lbeta）、Galbeta1-4GlcNAc（II）、Galbeta1-3GlcNAc（I）、Galbeta1-3GalNAcalpha1-（Talpha）、Galbeta1-3GalNAcbeta1-（Tbeta）、Galalpha1-3Gal（B）、Galalpha1-4Gal（E）、GalNAcbeta1-3Gal（P）、GalNAcalpha1-Ser/Thr（Tn）和GalNAcbeta1-4Gal（S）具有广泛的亲和力。在所测试的多价糖表位中，蓖麻毒素与含II型糖蛋白（gp）反应最佳。它与几种T（汤姆森-弗里德赖希）、肿瘤相关Tn以及含血型Sd（a+）的gp也反应良好。除了燕窝糖蛋白和Tamm-Horsfall糖蛋白（THGP）外，这种凝集素与ABH血型糖蛋白和唾液酸化糖蛋白反应微弱或根本不反应。根据目前和以往的结果，可以得出以下结论：（i）这些凝集素结构域的结合位点应为浅沟型，以Galbeta1-4Glcbeta1-和Galbeta1-3（4）GlcNAcbeta-作为主要结合位点；（ii）其大小可能与四糖一样大，且与乳糖-N-四糖（Galbeta1-3GlcNAc beta1-3Galbeta1-4Glc）和乳糖-N-新四糖（Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc）最互补；（iii）一般来说，糖表位的多价性会增强结合；（iv）在糖容纳结合位点附近的疏水相互作用增加了对Galbeta-的亲和力。本研究应有助于理解生物过程中碳水化合物-毒素相互作用所涉及的糖识别因子。应研究多价P/S糖表位对蓖麻毒素结合的影响。然而，由于缺乏合适的试剂，这一研究受到了阻碍。
