Matsuda T, Nagasawa S, Koide T, Koyama J
J Biochem. 1985 Jul;98(1):229-36. doi: 10.1093/oxfordjournals.jbchem.a135262.
We have investigated the limited proteolysis of the third component of complement, C3, by a human leukocyte protease, cathepsin G, by using a chemically modified C3, which was prepared by treatment of C3 with methylamine and a fluorescent thiol reagent, N-(dimethylamino-4-methylcoumarinyl)-maleimide (DACM) and was thus named DACM-C3me. Although native C3 was hardly cleaved by cathepsin G, DACM-C3me was cleaved by cathepsin G into three major fragments, which were termed C3c-G (150,000 daltons, 150 kd), C3d-G (25 kd), and C3a-G (10 kd). C3c-G was composed of four disulfide-linked polypeptide chains of 75 kd, 35 kd, and two 25 kd. C3d-G and C3a-G were single-chain fragments derived from the alpha chain. The N-terminal sequence of C3d-G was determined as Thr-Glu-Asp-Ala-Val-, suggesting that cathepsin G released C3d-G by cleaving a Met-Thr peptide bond which is located at 19 residues toward the N-terminal from the cysteinyl residue forming an internal thiolester linkage in native C3. C3d-G, like C3d-K (a C3d fragment produced by the action of plasma kallikrein), was found to have bioactivities such as leukocytosis-inducing and immunosuppressive activities.
我们使用一种化学修饰的C3研究了人类白细胞蛋白酶组织蛋白酶G对补体第三成分C3的有限蛋白水解作用。该化学修饰的C3是通过用甲胺和荧光硫醇试剂N-（二甲基氨基-4-甲基香豆素基）-马来酰亚胺（DACM）处理C3制备的，因此被命名为DACM-C3me。尽管天然C3几乎不被组织蛋白酶G切割，但DACM-C3me被组织蛋白酶G切割成三个主要片段，分别称为C3c-G（150,000道尔顿，150kd）、C3d-G（25kd）和C3a-G（10kd）。C3c-G由四条75kd、35kd和两条25kd的二硫键连接的多肽链组成。C3d-G和C3a-G是源自α链的单链片段。C3d-G的N端序列被确定为苏氨酸-谷氨酸-天冬氨酸-丙氨酸-缬氨酸-，这表明组织蛋白酶G通过切割一个位于天然C3中形成内部硫酯键的半胱氨酸残基N端19个残基处的甲硫氨酸-苏氨酸肽键释放出C3d-G。发现C3d-G与C3d-K（血浆激肽释放酶作用产生的C3d片段）一样，具有诱导白细胞增多和免疫抑制等生物活性。
