Structure and dynamic association of an assembly platform subcomplex of the bacterial type II secretion system

Type II secretion systems (T2SSs) allow diderm bacteria to secrete hydrolytic enzymes, adhesins, or toxins important for growth and virulence. To promote secretion of folded proteins, T2SSs assemble periplasmic filaments called pseudopili or endopili at an inner membrane subcomplex, the assembly pla...

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Published in:Structure (London) 2023-02, Vol.31 (2), p.152-165.e7
Main Authors: Dazzoni, Régine, Li, Yuanyuan, López-Castilla, Aracelys, Brier, Sébastien, Mechaly, Ariel, Cordier, Florence, Haouz, Ahmed, Nilges, Michael, Francetic, Olivera, Bardiaux, Benjamin, Izadi-Pruneyre, Nadia
Format: Article
Language:English
Subjects:
assembly platform
Bacteria - metabolism
Bacterial Proteins - chemistry
Biochemistry, Molecular Biology
ferredoxin-like fold
Fimbriae, Bacterial - metabolism
Life Sciences
protein-protein interaction
Structural Biology
type II secretion system
Type II Secretion Systems - metabolism
type IV pili
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Summary:Type II secretion systems (T2SSs) allow diderm bacteria to secrete hydrolytic enzymes, adhesins, or toxins important for growth and virulence. To promote secretion of folded proteins, T2SSs assemble periplasmic filaments called pseudopili or endopili at an inner membrane subcomplex, the assembly platform (AP). Here, we combined biophysical approaches, nuclear magnetic resonance (NMR) and X-ray crystallography, to study the Klebsiella AP components PulL and PulM. We determined the structure and associations of their periplasmic domains and describe the structure of the heterodimer formed by their ferredoxin-like domains. We show how structural complementarity and plasticity favor their association during the secretion process. Cysteine scanning and crosslinking data provided additional constraints to build a structural model of the PulL-PulM assembly in the cellular context. Our structural and functional insights, together with the relative cellular abundance of its components, support the role of AP as a dynamic hub that orchestrates pilus polymerization. [Display omitted] •Structures of two proteins from a bacterial type II secretion system assembly platform•Each protein alone forms a homodimer, but together they assemble as a heterodimer•The X-ray and NMR heterodimer structures are compatible with membrane insertion•Heterodimer assembly validated by in vivo approaches is key for secretion Dazzoni et al. characterized two components of the assembly platform belonging to the bacterial secretion machinery that allows transport of active enzymes and toxins. They show how these proteins associate in the membrane and act as a dynamic hub driving the polymerization of a protein filament that is required for secretion.
ISSN:0969-2126
1878-4186
DOI:10.1016/j.str.2022.12.003