Kim S, Narayana S V, Volanakis J E
Department of Medicine, University of Alabama at Birmingham 35294-0006, USA.
J Biol Chem. 1995 Oct 13;270(41):24399-405. doi: 10.1074/jbc.270.41.24399.
Complement factor D is a serine protease regulated by a novel mechanism that depends on conformational changes rather than cleavage of a zymogen for expression of proteolytic activity. The conformational changes are presumed to be induced by the single natural substrate, C3bB, and to result in reversible reorientation of the catalytic center and of the substrate binding site of factor D, both of which have atypical conformations. Here we report that replacement of Ser94, Thr214, and Ser215 of factor D (chymotrypsinogen numbering has been used for comparison purposes) with the corresponding residues of trypsin, Tyr, Ser, and Trp, is sufficient to induce substantially higher catalytic activity associated with a typical serine protease alignment of the catalytic triad residues His57, Asp102, and Ser195. These results provide a partial structural explanation for the low reactivity of "resting-state" factor D toward synthetic substrates.
补体因子D是一种丝氨酸蛋白酶，其受一种新机制调控，该机制依赖于构象变化而非通过酶原裂解来表达蛋白水解活性。推测构象变化由单一天然底物C3bB诱导产生，并导致因子D催化中心和底物结合位点发生可逆重排，这两者均具有非典型构象。在此我们报道，将因子D的Ser94、Thr214和Ser215（为便于比较使用了胰凝乳蛋白酶原编号）替换为胰蛋白酶的相应残基Tyr、Ser和Trp，足以诱导出与催化三联体残基His57、Asp102和Ser195的典型丝氨酸蛋白酶排列相关的显著更高的催化活性。这些结果为“静止状态”因子D对合成底物的低反应性提供了部分结构解释。
