摘要
Diderm bacteria,characterized by an additional lipid membrane layer known as the outer membrane,fold their outer membrane proteins(OMPs)via theβ-barrel assembly machinery(BAM)complex.Understanding how the BAM complex,particularly its key component BamA,assists in OMP folding remains crucial in bacterial cell biology.Recent research has focused primarily on the structural and functional characteristics of BamA within the Gracilicutes clade,such as in Escherichia coli(E.coli).However,another major evolutionary branch,Terrabacteria,has received comparatively less attention.An example of a Terrabacteria is Deinococcus radiodurans(D.radiodurans),a Gram-positive bacterium that possesses a distinctive outer membrane structure.In this study,we first demonstrated that theβ-barrel domains of BamA are not interchangeable between D.radiodurans and E.coli.The structure of D.radiodurans BamA was subsequently determined at 3.8Åresolution using cryo-electron microscopy,revealing obviously distinct arrangements of extracellular loop 4(ECL4)and ECL6 after structural comparison with their counterparts in gracilicutes.Despite the overall similarity in the topology of theβ-barrel domain,our results indicate that certain ECLs have evolved into distinct structures between the Terrabacteria and Gracilicutes clades.While BamA and its function are generally conserved across diderm bacterial species,our findings underscore the evolutionary diversity of this core OMP folder among bacteria,offering new insights into bacterial physiology and evolutionary biology.
双膜细菌除细胞质膜外,还具有一层额外的脂质膜,被称为细菌外膜。细菌外膜蛋白(OMPs)需要利用β-桶装配机器(BAM)复合体来辅助其折叠。理解BAM复合体(尤其是关键组分BamA)辅助OMP折叠的分子机制是细菌细胞生物学研究的关键问题。当前的研究主要集中在以大肠埃希氏菌为代表的薄壁菌(Gracilicutes)的BAM复合体。细菌的另外一个进化分支大地菌(Terrabacteria)也包括一些双膜细菌,然而对于其BAM复合体的结构和功能研究相对较少。耐辐射奇球菌(Deinococcus radiodurans,D.radiodurans)是一种具有较厚细胞壁,属于大地菌的双膜细菌。在本研究中,我们首先证明了耐辐射奇球菌和大肠埃希氏菌之间的BamA的β桶结构域不可互换。然后,我们解析了耐辐射奇球菌BamA的冷冻电镜结构,其分辨率为3.8Å。我们将它与薄壁菌中的同源蛋白进行结构比对后,发现其细胞外环4(ECL4)和细胞外环6(ECL6)展现出了明显的结构差异。这一结构观察表明,虽然BamA蛋白及其功能在双膜细菌的物种中普遍保守,但BamA的核心β桶结构域在细菌中呈现出多样性,为细菌生理学和进化生物学提供了新的视角。
基金
supported by the Fundamental Research Funds for the Central Universities(WK9100000063)
the Fundamental Research Funds for the Central Universities(WK9100000031)
the National Natural Science Foundation of China(32270035,32271241)
the Anhui Provincial Natural Science Foundation(2208085MC40,2008085QC98)
the Talent Fund Project of Biomedical Sciences and Health Laboratory of Anhui Province,University of Science and Technology of China(BJ9100000003)
the start-up funding from the University of Science and Technology of China(KY9100000034,KJ2070000082).
