Roa M, Boquet P
J Biol Chem. 1985 Jun 10;260(11):6827-35.
Two main polypeptides, Mr about 27,000 and 21,000, were protected against pepsin proteolysis when a mixture consisting of asolectin vesicles and 125I-labeled tetanus toxin was subjected to a pH drop from 7.2 to 3.0. The same result was obtained with the amino-terminal portion of the toxin (called fragment B). These polypeptides were not found to be protected in the following conditions: (i) when vesicles were omitted from the mixture; (ii) when the external pH of the vesicles was maintained at 7.2 and trypsin was used as a proteolytic agent; and (iii) when the vesicles were ruptured either before or after addition of the toxin. By specific immunoprecipitation, we identified the protected polypeptides as part of the central fragment of tetanus toxin. In addition, a 15.5-kDa polypeptide, belonging to toxin fragment C, was shown to be particularly resistant to digestion by various proteases, even in the absence of lipid vesicles. Based on these findings, we propose a model for entry of tetanus toxin into its target cells.
当由大豆卵磷脂囊泡和125I标记的破伤风毒素组成的混合物pH从7.2降至3.0时，有两种主要的多肽（分子量约为27,000和21,000）受到胃蛋白酶消化的保护。毒素的氨基末端部分（称为片段B）也得到了相同的结果。在以下条件下未发现这些多肽受到保护：（i）混合物中省略囊泡时；（ii）囊泡的外部pH维持在7.2且使用胰蛋白酶作为蛋白水解剂时；以及（iii）在添加毒素之前或之后囊泡破裂时。通过特异性免疫沉淀，我们将受保护的多肽鉴定为破伤风毒素中央片段的一部分。此外，即使在没有脂质囊泡的情况下，属于毒素片段C的一种15.5 kDa的多肽也显示出对各种蛋白酶的消化具有特别的抗性。基于这些发现，我们提出了破伤风毒素进入其靶细胞的模型。
