Korczynska Magdalena, Mukhtar Tariq A, Wright Gerard D, Berghuis Albert M
Department of Biochemistry, McGill University, Montreal, QC, Canada H3A 4A2.
Proc Natl Acad Sci U S A. 2007 Jun 19;104(25):10388-93. doi: 10.1073/pnas.0701809104. Epub 2007 Jun 11.
The streptogramin combination therapy of quinupristin-dalfopristin (Synercid) is used to treat infections caused by bacterial pathogens, such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. However, the effectiveness of this therapy is being compromised because of an increased incidence of streptogramin resistance. One of the clinically observed mechanisms of resistance is enzymatic inactivation of the type B streptogramins, such as quinupristin, by a streptogramin B lyase, i.e., virginiamycin B lyase (Vgb). The enzyme catalyzes the linearization of the cyclic antibiotic via a cleavage that requires a divalent metal ion. Here, we present crystal structures of Vgb from S. aureus in its apoenzyme form and in complex with quinupristin and Mg2+ at 1.65- and 2.8-A resolution, respectively. The fold of the enzyme is that of a seven-bladed beta-propeller, although the sequence reveals no similarity to other known members of this structural family. Quinupristin binds to a large depression on the surface of the enzyme, where it predominantly forms van der Waals interactions. Validated by site-directed mutagenesis studies, a reaction mechanism is proposed in which the initial abstraction of a proton is facilitated by a Mg2+ -linked conjugated system. Analysis of the Vgb-quinupristin structure and comparison with the complex between quinupristin and its natural target, the 50S ribosomal subunit, reveals features that can be exploited for developing streptogramins that are impervious to Vgb-mediated resistance.
链阳菌素联合疗法中的奎奴普丁-达福普汀（Synercid）用于治疗由细菌病原体引起的感染，如耐甲氧西林金黄色葡萄球菌和耐万古霉素屎肠球菌。然而，由于链阳菌素耐药性的发生率增加，这种疗法的有效性正受到损害。临床上观察到的耐药机制之一是B型链阳菌素（如奎奴普丁）被链阳菌素B裂解酶（即维吉尼亚霉素B裂解酶，Vgb）酶促失活。该酶通过需要二价金属离子的裂解催化环状抗生素的线性化。在此，我们分别展示了来自金黄色葡萄球菌的Vgb的无酶形式以及与奎奴普丁和Mg2+形成复合物的晶体结构，分辨率分别为1.65 Å和2.8 Å。尽管该酶的序列与这个结构家族的其他已知成员没有相似性，但其折叠方式为七叶β-螺旋桨。奎奴普丁结合在酶表面的一个大凹陷处，在那里它主要形成范德华相互作用。通过定点诱变研究验证，提出了一种反应机制，其中质子的初始提取由Mg2+连接的共轭体系促进。对Vgb-奎奴普丁结构的分析以及与奎奴普丁及其天然靶点50S核糖体亚基之间复合物的比较，揭示了可用于开发对Vgb介导的耐药性具有抗性的链阳菌素的特征。
