Structural basis of Cfr-mediated resistance to antibiotics targeting the bacterial ribosome

摘要 核糖体是一个基本的药物靶点，因为许多种类的临床重要抗生素与其功能相结合。 集中并干扰蛋白质合成的不同方面。在几个功能中心中，催化 肽基转移酶中心(PTC)是几种化学物质中最广泛的靶向抑制剂 上课。对这种PTC作用药物最丰富和临床相关的耐药机制之一 是基于CFR对23S rRNA的腺嘌呤残基2503(A2503)的C8位的甲基化 甲基转移酶。这种修饰使其对多种PTC靶向抗生素产生抗药性，包括 苯尼考、林可酰胺、恶唑烷酮、胸膜多菌素和链球菌A(PhLOPSa表型) 作为16元大环内酯类和潮霉素A，CFR介导的耐药性是一个令人担忧的医疗保健问题 由于cfr基因在致病菌中的快速传播而造成的威胁使许多临床上具有重要意义。 抗生素对抗感染治疗无效。因此，开发下一代PTC靶向抑制剂 对CFR阳性病原体采取行动具有极其重要的医学意义。虽然这个问题是可以解决的 通过结构驱动的合理药物设计，CFR修饰的核糖体的结构目前尚不清楚。 在拟议的项目中，我们将通过确定第一个高分辨率X射线晶体结构来解决这个问题 CFR修饰的细菌核糖体的分离或与显示出残留活性的抗生素的复合体 A2503甲基化核糖体。为了实现这一目标，我们将优化功能活性CFR的表达 嗜热菌Thermus thermophilus细胞中的甲基转移酶，已广泛用作 适合于结晶学研究的核糖体的来源。我们发现，尽管增长速度最快，但 65-72°C，嗜热梭菌也可以在显著较低的温度(48°C)下生长。通过克隆和表达CFR- 高温(65℃-65℃)中嗜热杆菌甲基转移酶基因的研究 72℃)，或通过在还原生长的嗜热链霉菌宿主中表达来自中嗜性细菌的erm基因 温度(48-65°C)，我们将获得带有甲基化A2503的可结晶核糖体。一旦它的结构 A2503-甲基化核糖体被确定，我们将在 与几种PTC作用药物的复合体，这些药物与修饰的核糖体显示出剩余的结合亲和力。这个 由此得到的信息将有助于理解CFR介导的抗性的分子原理 并将指导后续抗CFR阳性病原体的新抗菌药物的合理设计。 此外，在拟议项目成功完成后，我们将回答一个长期存在的基本问题 和医学相关的问题：如何在2.5-丙二醛中的单个核苷酸上添加一个甲基 核糖体导致对许多化学上无关的PTC靶向抗生素的耐药性？

SUMMARY The ribosome is an essential drug target as many classes of clinically important antibiotics bind to its functional centers and interfere with different aspects of protein synthesis. Out of several functional centers, the catalytic peptidyl transferase center (PTC) is targeted by the broadest array of inhibitors belonging to several chemical classes. One of the most abundant and clinically relevant mechanisms of resistance to such PTC-acting drugs is based on the methylation of the C8-position of an adenine residue 2503 (A2503) of the 23S rRNA by Cfr methyltransferase. This modification confers resistance to a wide range of PTC-targeting antibiotics, including phenicols, lincosamides, oxazolidinones, pleuromutilins, and streptogramins A (PhLOPSa phenotype), as well as 16-membered macrolides and hygromycin A. The Cfr-mediated drug resistance is an alarming healthcare threat because of the rapid spread of the cfr gene among pathogenic bacteria renders many clinically important antibiotics ineffective for anti-infection therapies. Thus, developing next-generation PTC-targeting inhibitors acting against the Cfr-positive pathogens is of utmost medical importance. While this problem could be tackled by structure-driven rational drug design, a structure of the Cfr-modified ribosome is currently unknown. In the proposed project, we will solve this problem by determining the first high-resolution X-ray crystal structure of the Cfr-modified bacterial ribosome in isolation or in complex with antibiotics exhibiting residual activity against the A2503-methylated ribosome. To achieve this goal, we will optimize the expression of functionally-active Cfr methyltransferases in the cells of thermophilic bacterium Thermus thermophilus, which has been widely used as the source of ribosomes suitable for crystallographic studies. We have found that in spite of growing optimally at 65-72°C, T. thermophilus can also grow at notably lower temperatures (48°C). By cloning and expressing Cfr- methyltransferase genes from moderately thermophilic bacteria in T. thermophilus at high temperatures (65- 72°C) or by expressing the erm genes from the mesophilic bacteria in the T. thermophilus host grown at reduced temperatures (48-65°C), we will obtain crystallizable ribosomes with methylated A2503. Once the structure of the A2503-methylated ribosome is determined, we will solve the structures of this Cfr-modified ribosome in complex with several PTC-acting drugs exhibiting residual binding affinity for the modified ribosome. The resulting information will be instrumental for understanding the molecular principles of Cfr-mediated resistance and will instruct the subsequent rational design of new antibacterials active against Cfr-positive pathogens. Moreover, upon successful completion of the proposed project, we shall answer a long-standing fundamental and medically relevant question: How the addition of a methyl group to a single nucleotide in the 2.5-MDa ribosome results in resistance to many classes of chemically-unrelated PTC-targeting antibiotics?