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Periplasmic inner membrane ring of the Shigella type 3 secretion system
Structural highlights
FunctionMXIG_SHIFL Involved in the secretion of the Ipa antigens. Involved in the intracellular dissemination of Shigella. Part of the Mxi-Spa secretion apparatus. Publication Abstract from PubMedThe Type III Secretion Systems (T3SS) needle complex is a conserved syringe-shaped protein translocation nanomachine with a mass of about 3.5 MDa essential for the survival and virulence of many Gram-negative bacterial pathogens. This system is composed of a membrane-embedded basal body and an extracellular needle that deliver effector proteins into host cells. High-resolution structures of the T3SS from different organisms and infection stages are needed to understand the underlying molecular mechanisms of effector translocation. Here, we present the cryo-electron microscopy structure of the isolated Shigella T3SS needle complex. The inner membrane (IM) region of the basal body adopts 24-fold rotational symmetry and forms a channel system that connects the bacterial periplasm with the export apparatus cage. The secretin oligomer adopts a heterogeneous architecture with 16- and 15-fold cyclic symmetry in the periplasmic N-terminal connector and C-terminal outer membrane ring, respectively. Two out of three IM subunits bind the secretin connector via a beta-sheet augmentation. The cryo-EM map also reveals the helical architecture of the export apparatus core, the inner rod, the needle and their intervening interfaces. Cryo-EM structure of the Shigella type III needle complex.,Lunelli M, Kamprad A, Burger J, Mielke T, Spahn CMT, Kolbe M PLoS Pathog. 2020 Feb 24;16(2):e1008263. doi: 10.1371/journal.ppat.1008263. PMID:32092125[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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