Direct Visualization by Cryo-EM of the Mycobacterial Capsular Layer: A Labile Structure Containing ESX-1-Secreted Proteins

PLoS Pathogens

Mamadou Daffé¹  Brigitte Wever²  Wilbert Bitter²  Ben J. Appelmelk²  Edith N. G. Houben²  Jeroen Geurtsen²  Connie R. Jiménez³  Sander R. Piersma³  Maaike van Zon⁴  Musa Sani⁴  Jason Pierson⁴  Karin de Punder⁴  Peter J. Peters⁴  Nicole van der Wel⁴ 

[1] CNRS, Institut de Pharmacologie et de Biologie Structurale, Département Mécanismes Moléculaires des Infections Mycobactériennes, Toulouse, France;Department of Medical Microbiology and Infection Control, VU University Medical Centre, Amsterdam, the Netherlands;Department of Medical Oncology, VU University Medical Centre, Amsterdam, the Netherlands;Division of Cell Biology-B6, Netherlands Cancer Institute–Antoni van Leeuwenhoek Hospital (NKI-AVL), Amsterdam, the Netherlands

关键词: Mycobacterium tuberculosis;    Cell membranes;    Mycobacterium bovis;    Detergents;    Macrophages;    Protein extraction;    Cytokines;    Outer membrane proteins;   

DOI  :  10.1371/journal.ppat.1000794

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

The cell envelope of mycobacteria, a group of Gram positive bacteria, is composed of a plasma membrane and a Gram-negative-like outer membrane containing mycolic acids. In addition, the surface of the mycobacteria is coated with an ill-characterized layer of extractable, non-covalently linked glycans, lipids and proteins, collectively known as the capsule, whose occurrence is a matter of debate. By using plunge freezing cryo-electron microscopy technique, we were able to show that pathogenic mycobacteria produce a thick capsule, only present when the cells were grown under unperturbed conditions and easily removed by mild detergents. This detergent-labile capsule layer contains arabinomannan, α-glucan and oligomannosyl-capped glycolipids. Further immunogenic and proteomic analyses revealed that Mycobacterium marinum capsule contains high amounts of proteins that are secreted via the ESX-1 pathway. Finally, cell infection experiments demonstrated the importance of the capsule for binding to cells and dampening of pro-inflammatory cytokine response. Together, these results show a direct visualization of the mycobacterial capsular layer as a labile structure that contains ESX-1-secreted proteins.

【 授权许可】

CC BY