Deciphering the molecular mechanisms of sterol lipid trafficking in bacteria

项目概要/摘要 包括胆固醇在内的硬脂酸脂质对哺乳动物细胞生理学很重要。这些分子 调节生物膜的流动性并因此涉及维持膜的完整性， 类固醇还参与细胞内和细胞间的信号传导，并被运输到 到亚细胞膜。然而几十年的研究已经提供了真核固醇的分子见解 合成，运输，调节和功能，细菌和古细菌缺乏对甾醇的类似理解。 虽然人们认为古生菌不制造或使用甾醇，但一些细菌确实制造和运输甾醇;许多细菌都不使用甾醇。 其他已知与由真核生物产生的甾醇结合。这些细菌包括致病性 螺旋体（伯氏疏螺旋体、苍白密螺旋体）、分枝杆菌、衣原体、立克次体和肠道 微生物群对于病原体来说，从宿主获得甾醇是至关重要的，因为它们定殖并构建它们的 手机信封对于肠道微生物来说，与胆固醇的相互作用可以改变宿主的脂质代谢， 导致心脏代谢疾病和血脂异常。尽管有大量关于 微生物与这些脂质的相互作用，缺乏对相互作用如何发生以及如何发生的分子见解。 它们是受管制的。我们将解决这一知识差距，我们将揭示新的治疗目标， 干预细菌定植和异常固醇脂质代谢。 考虑到有些细菌会重新产生甾醇，我们推断， 在制造它们的细菌中的处理可以揭示它们在使用它们的细菌中的处理。我们 因此，集中于近40年前报道的产生固醇的细菌--荚膜甲基球菌。 最近的研究报道了M.囊状的此后，我们增加了 与这些报告相比，一份报告显示固醇贩运也有很大不同。我们发现了三种蛋白质， 交通固醇：BstA、BstB和BstC。BstA是耐药转运蛋白家族中的一员 作为多种细菌代谢物的转运体。BstB是周质结合蛋白， 参与膦酸盐运输的同系物。最后，BstC是外膜相关脂蛋白， 属于其底物未知的转运蛋白家族。Bst蛋白的整体结构 与真核固醇转运蛋白有显著不同。然而，它们都含有类似的配体位点， 疏水和亲水残基的呈现。我们认为一种改良的结构基因组学 其中焦点在于配体位点而不是整体结构/序列的方法将使得能够 细菌中功能同源蛋白的鉴定。这项工作将利用生物信息学，定量配体 结合分析和结构方法来鉴定和表征细菌中的甾醇运输蛋白， 制造甾醇、劫持甾醇的病原体和调节宿主甾醇代谢的肠道植物群。

Project summary/abstract Sterols lipids, including cholesterol, are important for mammalian cell physiology. These molecules modulate the fluidity of biological membranes and are therefore implicated maintaining membrane integrity, stress tolerance, fusion events, etc. Sterols are also involved in intra- and intercellular signaling and are trafficked to sub-cellular membranes. Whereas decades of research have provided molecular insights into eukaryotic sterol synthesis, transport, regulation, and function, similar understanding of sterols is lacking for bacteria and archaea. While it is thought that archaea do not make or use sterols, some bacteria do make and transport sterols; many others are known to engage with sterols produced by eukaryotes. These bacteria include the pathogenic spirochetes (Borrelia burgdorferi, Treponema pallidum), Mycobacteria, Chlamydia, Rickettsia, and gut microbiota. For pathogens, the acquisition of sterols from the host is critical as they colonize and construct their cell envelopes. For gut microbes, interactions with cholesterol can alter the host lipid metabolism, thereby contributing to cardiometabolic diseases and dyslipidemia. Despite the preponderance of research about microbial interactions with these lipids, lacking are molecular insights into how the interactions occur and how they are regulated. We will address this knowledge gap, which we posit will reveal novel targets for therapeutic interventions in bacterial colonization and aberrant sterol lipid metabolism. Given that some bacteria produce sterols de novo, we reasoned that achieving an understanding of sterol handling in bacteria that make them could reveal insights into their handling in bacteria that use them. We therefore focused on Methylcoccus capsulatus, a bacterium reported to produce sterols nearly 40 years ago. Recent studies reported a significant divergence in sterol biosynthesis in M. capsulatus. We have since added to those reports one showing that sterol trafficking is also substantially different. We identified three proteins that traffic sterols: BstA, BstB, and BstC. BstA is a member of the resistance nodulation division family of transporters that work as transporters for a wide range of bacterial metabolites. BstB is a periplasmic binding protein with homologs involved in phosphonate transport. Finally, BstC is an outer membrane associated lipoprotein belonging to a family of transporters whose substrates are not known. The overall structures of the Bst proteins are markedly different from eukaryotic sterol transporters. However, they all contain ligand sites that are similar in the presentation of hydrophobic and hydrophilic residues. We posit that a modified structural genomics approach wherein the focus is on ligand sites instead of overall structure/sequence would enable the identification of functionally homologous proteins in bacteria. This work will use bioinformatics, quantitative ligand binding analyses, and structural approaches to identify and characterize sterol trafficking proteins in bacteria that make sterols, pathogens that hijack sterols, and gut flora that modulate host sterol metabolism.