Specificity, structure and function of the lantibiotic immunity proteins SpaI and NisI

lantibiotic是一种多肽抗生素，含有特有的硫代氨酸环结构。它们是核糖体合成和翻译后修饰的。来自枯草芽孢杆菌的抗生素subtilin和来自乳酸乳球菌的抗生素ninin的作用方式是基于与细胞壁前体脂质II结合并形成多粒lantibiotic/脂质II膜复合物。Lantibiotic生产者对自身的Lantibiotic敏感，因此它们表达一种膜结合LanI免疫蛋白和一种独立的abc转运蛋白复合物。LanI介导免疫的作用方式和分子机制尚不清楚。虽然枯草菌素和nisin具有相似的分子结构，但各自的免疫蛋白NisI和SpaI对各自的抗生素具有高度选择性。我们可以在溶液中解析SpaI的核磁共振结构，具有迄今未知的折叠模式。到目前为止，还无法从该结构中得出关于免疫机制的结论。目前，我们考虑了四种可能的SpaI介导免疫的机制，我们希望在项目中验证：(A) LanI蛋白在l抗生素到达细胞质膜之前捕获l抗生素（捕获功能），(B) LanI蛋白与l抗生素/脂质II孔相互作用以阻止孔形成（复杂抑制），(C) LanI相互作用并破坏现有的l抗生素/脂质II孔（孔破坏），(D) SpaI蛋白封闭现有的l抗生素/脂质II孔（孔密封）。本项目旨在运用分子生物学、生物化学和生物物理等方法，通过比较功能同源和结构最可能不同的免疫蛋白，了解SpaI和NisI蛋白的分子机制、高特异性和膜相互作用。了解SpaI免疫的分子机制和特异性对于可能应用具有改变抗生素活性的nisin和subtilin变体也很重要。

Lantibiotics are peptide antibiotics containing characteristic lanthionine ring structures. They are ribosomally synthesized and post-translationally modified. The antibiotic mode of action of lantibiotics subtilin from Bacillus subtilis and ninin from Lactococcus lactis are based on the binding to the cell wall precursor lipid II and the formation of multimere lantibiotic/lipid II membrane complexes. Lantibiotic producers are sensitive against their own lantibiotic and therefore they express a membrane bound LanI immunity protein and an independent ABC-transporter complex. The mode of action and the molecular mechanism of LanI mediated immunity are still unknown. Although subtilin and nisin have a similar molecular structure, the respective immunity proteins NisI and SpaI are highly selective for the respective antibiotic. We could resolve the NMR-structure of SpaI in solution, with a so far unknown folding pattern. No conclusions on the immunity mechanism could be drawn form the structure so far. At present we consider four possible mechanisms for SpaI mediated immunity, which we want to verify during the project: (A) LanI proteins capture lantibiotics before they reach the cytoplasma membrane (capture function), (B) LanI proteins interact with lantibiotic/lipid II pores to prevent pore formation (complex inhibition), (C) LanI interact and destroy existing lantibiotic/lipid II pores (pore destruction), and (D) SpaI protein seal existing lantibiotic/lipid II pores (pore sealing). Aim of the project is to understand the molecular mechanisms, the high specificity and the membrane interaction of SpaI and NisI proteins by comparing the functional homologue and structural most likely different immunity proteins, using molecular biological, biochemical and biopyhysical methods. Understanding the molecular mechanism and the specificity of SpaI immunity is also important for a possible application of nisin and subtilin variants with altered antibiotic activities.