变形菌表面脂蛋白的单分子动力学研究表明其具有相似性和协同性。
Single-molecule dynamics of surface lipoproteins in bacteroides indicate similarities and cooperativity.
机构信息
Department of Chemistry, University of Michigan, Ann Arbor, Michigan.
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan.
出版信息
Biophys J. 2022 Dec 6;121(23):4644-4655. doi: 10.1016/j.bpj.2022.10.024. Epub 2022 Oct 20.
The gut microbiota comprises hundreds of species with a composition shaped by the available glycans. The well-studied starch utilization system (Sus) is a prototype for glycan uptake in the human gut bacterium Bacteroides thetaiotaomicron (Bt). Each Sus-like system includes outer-membrane proteins, which translocate glycan into the periplasm, and one or more cell-surface glycoside hydrolases, which break down a specific (cognate) polymer substrate. Although the molecular mechanisms of the Sus system are known, how the Sus and Sus-like proteins cooperate remains elusive. Previously, we used single-molecule and super-resolution fluorescence microscopy to show that SusG is mobile on the outer membrane and slows down in the presence of starch. Here, we compare the dynamics of three glycoside hydrolases: SusG, Bt4668, and Bt1760, which target starch, galactan, and levan, respectively. We characterized the diffusion of each surface hydrolase in the presence of its cognate glycan and found that all three enzymes are mostly immobile in the presence of the polysaccharide, consistent with carbohydrate binding. Moreover, experiments in glucose versus oligosaccharides suggest that the enzyme dynamics depend on their expression level. Furthermore, we characterized enzyme diffusion in a mixture of glycans and found that noncognate polysaccharides modify the dynamics of SusG and Bt1760 but not Bt4668. We investigated these systems with polysaccharide mixtures and genetic knockouts and found that noncognate polysaccharides modify hydrolase dynamics through some combination of nonspecific protein interactions and downregulation of the hydrolase. Overall, these experiments extend our understanding of how Sus-like lipoprotein dynamics can be modified by changing carbohydrate conditions and the expression level of the enzyme.
肠道微生物群落由数百种物种组成,其组成受可利用糖的影响。研究充分的淀粉利用系统(Sus)是人类肠道细菌拟杆菌(Bt)中糖摄取的原型。每个类似 Sus 的系统都包括外膜蛋白,它将聚糖转运到周质中,以及一个或多个细胞表面糖苷水解酶,它分解特定的(同源)聚合物底物。尽管 Sus 系统的分子机制是已知的,但 Sus 和类似 Sus 的蛋白如何合作仍然难以捉摸。以前,我们使用单分子和超分辨率荧光显微镜表明,SusG 在质膜上是可移动的,并在淀粉存在下减慢速度。在这里,我们比较了三种糖苷水解酶的动力学:SusG、Bt4668 和 Bt1760,它们分别针对淀粉、半乳糖和果聚糖。我们在每种糖的存在下表征了每种表面水解酶的扩散,并发现所有三种酶在多糖存在下大部分是不移动的,这与碳水化合物结合一致。此外,在葡萄糖与低聚糖的实验表明,酶的动力学取决于它们的表达水平。此外,我们在糖混合物中表征了酶的扩散,并发现非同源多糖修饰了 SusG 和 Bt1760 的酶动力学,但不修饰 Bt4668。我们用多糖混合物和遗传敲除研究了这些系统,发现非同源多糖通过非特异性蛋白质相互作用和水解酶下调的某种组合来修饰水解酶动力学。总的来说,这些实验扩展了我们对类似 Sus 的脂蛋白动力学如何通过改变碳水化合物条件和酶的表达水平来修饰的理解。