Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA.
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA
J Bacteriol. 2019 Jun 10;201(13). doi: 10.1128/JB.00195-19. Print 2019 Jul 1.
Bacterial lipoproteins are globular proteins anchored to the extracytoplasmic surfaces of cell membranes through lipidation at a conserved N-terminal cysteine. Lipoproteins contribute to an array of important cellular functions for bacteria, as well as being a focal point for innate immune system recognition through binding to Toll-like receptor 2 (TLR2) heterodimer complexes. Although lipoproteins are conserved among nearly all classes of bacteria, the presence and type of α-amino-linked acyl chain are highly variable and even strain specific within a given bacterial species. The reason for lyso-lipoprotein formation and -acylation variability in general is presently not fully understood. In , lipoproteins are anchored by an -acyl--monoacyl-glyceryl cysteine (lyso form) moiety installed by a chromosomally encoded lipoprotein intramolecular transacylase (Lit). Here, we describe a mobile genetic element common to environmental isolates of and spp. encoding a functional Lit ortholog (Lit2) that is cotranscribed with several well-established copper resistance determinants. Expression of Lit2 is tightly regulated, and induction by copper converts lipoproteins from the diacylglycerol-modified form characteristic of type strains to the α-amino-modified lyso form observed in Conversion to the lyso form through either copper addition to media or constitutive expression of decreases TLR2 recognition when using an activated NF-κB secreted embryonic alkaline phosphatase reporter assay. While lyso formation significantly diminishes TLR2 recognition, lyso-modified lipoprotein is still predominantly recognized by the TLR2/TLR6 heterodimer. The induction of lipoprotein N-terminal remodeling in response to environmental copper in Gram-positive bacteria suggests a more general role in bacterial cell envelope physiology. N-terminal modification by lyso formation, in particular, simultaneously modulates the TLR2 response in direct comparison to their diacylglycerol-modified precursors. Thus, use of copper as a frontline antimicrobial control agent and ensuing selection raises the potential of diminished innate immune sensing and enhanced bacterial virulence.
细菌脂蛋白通过保守的 N 端半胱氨酸的脂质化锚定在细胞质膜的细胞外表面。脂蛋白为细菌提供了一系列重要的细胞功能，并且通过与 Toll 样受体 2（TLR2）异二聚体复合物结合成为先天免疫系统识别的焦点。尽管脂蛋白在几乎所有细菌种类中都保守，但α-氨基酸连接的酰基链的存在和类型在给定细菌物种内高度可变，甚至菌株特异性。一般来说，脂脂蛋白形成和酰化变异性的原因目前还不完全清楚。在 中，脂蛋白通过由染色体编码的脂蛋白分子内转酰酶（Lit）安装的酰基-单酰基甘油半胱氨酸（脂形式）部分锚定。在这里，我们描述了一种在 和 环境分离株中常见的可移动遗传元件，该元件编码一种功能性 Lit 同源物（Lit2），它与几个已建立的铜抗性决定簇共转录。Lit2 的表达受到严格调控，铜的诱导将脂蛋白从典型的 型菌株的二酰基甘油修饰形式转换为在 中观察到的α-氨基酸修饰的脂形式。通过向培养基中添加铜或组成型表达 ，将脂蛋白转化为脂形式会降低使用激活的 NF-κB 分泌胚胎碱性磷酸酶报告测定法时 TLR2 的识别。虽然脂形成显著降低了 TLR2 的识别，但脂修饰的脂蛋白仍然主要被 TLR2/TLR6 异二聚体识别。革兰氏阳性菌对环境铜的反应诱导脂蛋白 N 端重塑表明其在细菌细胞包膜生理学中具有更普遍的作用。特别是通过脂形成进行 N 端修饰，与它们的二酰基甘油修饰前体相比，直接调节 TLR2 反应。因此，将铜用作一线抗菌控制剂并由此产生的选择增加了先天免疫感应减弱和细菌毒力增强的可能性。
