Jackson K W, Tang J
Biochemistry. 1982 Dec 21;21(26):6620-5. doi: 10.1021/bi00269a001.
The complete amino acid sequence of streptokinase has been determined by automated Edman degradation of its cyanogen bromide and proteolytic fragments. The protein consists of 415 amino acid residues. Sequence microheterogeneity was found at two positions. The NH2-terminal 245 residues of streptokinase are homologous to the sequences of several serine proteases including bovine trypsin and Streptomyces griseus proteases A and B. The sequence alignment suggests that the active-site histidine-57 has changed to a glycine in streptokinase. The other active-site residues, aspartyl-102 and serine-195, are, however, present at the expected positions. Streptokinase also contains internal sequence homology between the NH2-terminal 173 residues and a COOH-terminal 162-residue region between residues 254 and 415. Moderate homology in predicted secondary structures also exists between these two regions. Although streptokinase is not a protease, these observations suggest that it has evolved from a serine protease by gene duplication and fusion. A COOH-terminal region of about 80 residues is apparently deleted from the second half of the duplicated structures. These observations further suggest that the three-dimensional structure of streptokinase likely contains two independently folded domains, each homologous to serine proteases.
通过对链激酶的溴化氰裂解片段和蛋白水解片段进行自动Edman降解，已确定了链激酶完整的氨基酸序列。该蛋白质由415个氨基酸残基组成。在两个位置发现了序列微异质性。链激酶的氨基末端245个残基与包括牛胰蛋白酶以及灰色链霉菌蛋白酶A和B在内的几种丝氨酸蛋白酶的序列同源。序列比对表明，链激酶中活性位点的组氨酸-57已变为甘氨酸。然而，其他活性位点残基，天冬氨酸-102和丝氨酸-195，位于预期位置。链激酶在氨基末端173个残基与254至415位残基之间的羧基末端162个残基区域之间也存在内部序列同源性。这两个区域在预测的二级结构上也存在适度的同源性。尽管链激酶不是蛋白酶，但这些观察结果表明它是通过基因复制和融合从丝氨酸蛋白酶进化而来的。在重复结构的后半部分明显缺失了一个约80个残基的羧基末端区域。这些观察结果进一步表明，链激酶的三维结构可能包含两个独立折叠的结构域，每个结构域都与丝氨酸蛋白酶同源。
