Shackelford D A, Trowbridge I S
EMBO J. 1986 Dec 1;5(12):3275-80. doi: 10.1002/j.1460-2075.1986.tb04639.x.
The human interleukin-2 (IL-2) receptor was quantitatively cleaved into two large disulfide-bonded fragments by either trypsin or endoproteinase lys-C (endo lys-C). The smaller fragment contains both N-linked oligosaccharides found in the intact receptor and is derived from the amino terminus of the molecule. The larger proteolytic fragment was metabolically labeled with 32PO4 and represents the carboxy terminus. The predicted cleavage sites of both enzymes lie in the region of the molecule encoded by exon 3. This pattern of limited proteolysis provides biochemical evidence that the extracellular region of the receptor is organized into two domains. This supports a structural model of the receptor in which the regions of internal homology encoded by exons 2 and 4 form independent disulfide-bonded domains connected by a hydrophilic segment. To determine the role of these domains in IL-2 binding, [125I]IL-2 was chemically cross-linked to the proteolytically cleaved receptor on the cell surface. The 125I-labeled complex obtained displayed N-linked oligosaccharides and had an Mr consistent with one molecule of IL-2 cross-linked to the smaller proteolytic fragment of the receptor. Thus, the amino-terminal domain of the IL-2 receptor appears to form an integral part of the IL-2 binding site.
人白细胞介素-2（IL-2）受体可被胰蛋白酶或内肽酶赖氨酸-C（内肽酶赖氨酸-C）定量切割成两个由二硫键连接的大片段。较小的片段包含完整受体中发现的两个N-连接寡糖，且来源于分子的氨基末端。较大的蛋白水解片段用32PO4进行代谢标记，代表羧基末端。两种酶的预测切割位点都位于由外显子3编码的分子区域内。这种有限蛋白水解模式提供了生化证据，表明受体的细胞外区域被组织成两个结构域。这支持了受体的一种结构模型，其中由外显子2和4编码的内部同源区域形成由亲水片段连接的独立二硫键连接结构域。为了确定这些结构域在IL-2结合中的作用，将[125I]IL-2化学交联到细胞表面经蛋白水解切割的受体上。得到的125I标记复合物显示有N-连接寡糖，其分子量与一个IL-2分子交联到受体较小蛋白水解片段上相符。因此，IL-2受体的氨基末端结构域似乎构成了IL-2结合位点的一个组成部分。
