Isbilir Buse, Yeates Anna, Alva Vikram, Bharat Tanmay A M
Structural Studies Division, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom.
Department of Protein Evolution, Max Planck Institute for Biology Tübingen, Tübingen, Germany.
PLoS Biol. 2025 Apr 15;23(4):e3003130. doi: 10.1371/journal.pbio.3003130. eCollection 2025 Apr.
Corynebacterium glutamicum is a diderm bacterium extensively used in the industrial-scale production of amino acids. Corynebacteria belong to the bacterial family Mycobacteriaceae, which is characterized by a highly unusual cell envelope with an outer membrane consisting of mycolic acids, called mycomembrane. The mycomembrane is further coated by a surface (S-)layer array in C. glutamicum, making this cell envelope highly distinctive. Despite the biotechnological significance of C. glutamicum and biomedical significance of mycomembrane-containing pathogens, ultrastructural and molecular details of its distinctive cell envelope remain poorly characterized. To address this, we investigated the cell envelope of C. glutamicum using electron cryotomography and cryomicroscopy of focused ion beam-milled single and dividing cells. Our cellular imaging allowed us to map the different components of the cell envelope onto the tomographic density. Our data reveal that C. glutamicum has a variable cell envelope, with the S-layer decorating the mycomembrane in a patchy manner. We further isolated and resolved the structure of the S-layer at 3.1 Å-resolution using single particle electron cryomicroscopy. Our structure shows that the S-layer of C. glutamicum is composed of a hexagonal array of the PS2 protein, which interacts directly with the mycomembrane via an anchoring segment containing a coiled-coil motif. Bioinformatic analyses revealed that the PS2 S-layer is sparsely yet exclusively present within the Corynebacterium genus and absent in other genera of the Mycobacteriaceae family, suggesting distinct evolutionary pathways in the development of their cell envelopes. Our structural and cellular data collectively provide a topography of the unusual C. glutamicum cell surface, features of which are shared by many pathogenic and microbiome-associated bacteria, as well as by several industrially significant bacterial species.
谷氨酸棒杆菌是一种革兰氏阳性细菌，广泛用于氨基酸的工业规模生产。棒杆菌属于分枝杆菌科，其特点是具有高度不寻常的细胞包膜，外膜由分枝菌酸组成，称为霉菌膜。在谷氨酸棒杆菌中，霉菌膜进一步被表面（S）层阵列覆盖，使得这种细胞包膜非常独特。尽管谷氨酸棒杆菌具有生物技术意义，含霉菌膜的病原体具有生物医学意义，但其独特细胞包膜的超微结构和分子细节仍未得到充分表征。为了解决这个问题，我们使用聚焦离子束研磨的单个和分裂细胞的电子冷冻断层扫描和冷冻显微镜研究了谷氨酸棒杆菌的细胞包膜。我们的细胞成像使我们能够将细胞包膜的不同成分映射到断层扫描密度上。我们的数据表明，谷氨酸棒杆菌具有可变的细胞包膜，S层以斑驳的方式装饰霉菌膜。我们进一步使用单颗粒电子冷冻显微镜以3.1埃分辨率分离并解析了S层的结构。我们的结构表明，谷氨酸棒杆菌的S层由PS2蛋白的六边形阵列组成，该阵列通过包含卷曲螺旋基序的锚定段直接与霉菌膜相互作用。生物信息学分析表明，PS2 S层在棒杆菌属中稀疏但仅存在，在分枝杆菌科的其他属中不存在，这表明它们的细胞包膜在进化过程中有不同的途径。我们的结构和细胞数据共同提供了谷氨酸棒杆菌异常细胞表面的拓扑结构，其特征为许多致病和与微生物群相关的细菌以及几种具有工业重要性的细菌所共有。
