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Nat Struct Mol Biol. 2017 Feb;24(2):177-183. doi: 10.1038/nsmb.3350. Epub 2017 Jan 9.

Structural insights into the secretin translocation channel in the type II secretion system.

Yan Z1,2,3, Yin M1,2,3,4, Xu D5, Zhu Y5, Li X1,2,3,4.

Author information

1
School of Life Sciences, Tsinghua University, Beijing, China.
2
Advanced Innovation Center for Structural Biology, Tsinghua University, Beijing, China.
3
Ministry of Education Key Laboratory of Protein Sciences, Tsinghua University, Beijing, China.
4
Tsinghua-Peking Joint Center for Life Sciences, Beijing, China.
5
Life Sciences Institute and Innovation Center for Cell Signaling Network, Zhejiang University, Hangzhou, China.

Abstract

The secretin GspD of the type II secretion system (T2SS) forms a channel across the outer membrane in Gram-negative bacteria to transport substrates from the periplasm to the extracellular milieu. The lack of an atomic-resolution structure of the GspD channel hinders the investigation of substrate translocation mechanism of T2SS. Here we report cryo-EM structures of two GspD channels (∼1 MDa), from Escherichia coli K12 and Vibrio cholerae, at ∼3 Å resolution. The structures reveal a pentadecameric channel architecture, wherein three rings of GspD N domains form the periplasmic channel. The secretin domain constitutes a novel double β-barrel channel, with at least 60 β-strands in each barrel, and is stabilized by S domains. The outer membrane channel is sealed by β-strand-enriched gates. On the basis of the partially open state captured, we proposed a detailed gate-opening mechanism. Our structures provide a structural basis for understanding the secretin superfamily and the mechanism of substrate translocation in T2SS.

PMID:
28067918
DOI:
10.1038/nsmb.3350
[Indexed for MEDLINE]

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