Chen Yuhang, Song Gang, Jiang Fan, Feng Liang, Zhang Xiaoxuan, Ding Yi, Bartlam Mark, Yang Ao, Ma Xiang, Ye Sheng, Liu Yiwei, Tang Hong, Song Houyan, Rao Zihe
Laboratory of Structural Biology, MOE Laboratory of Protein Science, Tsinghua University, Beijing, China.
Eur J Biochem. 2002 Jan;269(2):705-11. doi: 10.1046/j.0014-2956.2001.02706.x.
Staphylokinase (SAK) is a 15.5-kDa protein from Staphylococcus aureus that activates plasminogen by forming a 1 : 1 complex with plasmin. Recombinant SAK has been shown in clinical trials to induce fibrin-specific clot lysis in patients with acute myocardial infarction. However, SAK elicits high titers of neutralizing antibodies. Biochemical and protein engineering studies have demonstrated the feasibility of generating SAK variants with reduced antigenicity yet intact thrombolytic potency. Here, we present X-ray crystallographic evidence that the SAK(S41G) mutant may assume a dimeric structure. This dimer model, at 2.3-A resolution, could explain a major antigenic epitope (residues A72-F76 and residues K135-K136) located in the vicinity of the dimer interface as identified by phage-display. These results suggest that SAK antigenicity may be reduced by eliminating dimer formation. We propose several potential mutation sites at the dimer interface that may further reduce the antigenicity of SAK.
葡萄球菌激酶（SAK）是一种来自金黄色葡萄球菌的15.5 kDa蛋白质，它通过与纤溶酶形成1:1复合物来激活纤溶酶原。重组SAK在临床试验中已显示可诱导急性心肌梗死患者发生纤维蛋白特异性血栓溶解。然而，SAK会引发高滴度的中和抗体。生化和蛋白质工程研究已证明产生抗原性降低但溶栓效力完整的SAK变体是可行的。在此，我们提供X射线晶体学证据表明SAK(S41G)突变体可能呈现二聚体结构。这个分辨率为2.3 Å的二聚体模型可以解释一个主要抗原表位（A72 - F76残基和K135 - K136残基），该表位位于通过噬菌体展示鉴定的二聚体界面附近。这些结果表明，通过消除二聚体形成可能降低SAK的抗原性。我们在二聚体界面提出了几个潜在的突变位点，这可能会进一步降低SAK的抗原性。
