Structural lessons on bacterial secretins

Barbat, Brice; Douzi, Badreddine; Voulhoux, Romé

doi:10.1016/j.biochi.2022.08.019

Cited by 6 publications

(7 citation statements)

References 66 publications

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“…The last two components (PilQ, PilW) are involved in making a gated portal in the OM for the emergence of the T4aP on the cell surface [86]. PilQ belongs to the secretin family of giant pores, found in a variety of systems, allowing various substrates to traverse the OM in diderms [87,88]. Structures of the T4aP secretin show a gated channel composed of 14 PilQ monomers, spanning the periplasm [89,90].…”

Section: T4apmentioning

confidence: 99%

Mechanism of assembly of type 4 filaments: everything you always wanted to know (but were afraid to ask)

Pelicic

2023

Microbiology

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Type 4 filaments (T4F) are a superfamily of filamentous nanomachines – virtually ubiquitous in prokaryotes and functionally versatile – of which type 4 pili (T4P) are the defining member. T4F are polymers of type 4 pilins, assembled by conserved multi-protein machineries. They have long been an important topic for research because they are key virulence factors in numerous bacterial pathogens. Our poor understanding of the molecular mechanisms of T4F assembly is a serious hindrance to the design of anti-T4F therapeutics. This review attempts to shed light on the fundamental mechanistic principles at play in T4F assembly by focusing on similarities rather than differences between several (mostly bacterial) T4F. This holistic approach, complemented by the revolutionary ability of artificial intelligence to predict protein structures, led to an intriguing mechanistic model of T4F assembly.

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Section: T4apmentioning

confidence: 99%

Mechanism of assembly of type 4 filaments: everything you always wanted to know (but were afraid to ask)

Pelicic

2023

Microbiology

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“…Here, 15:12 and 15:24 stoichiometries have been observed between the C-modules and their IM partners, respectively (Chernyatina and Low, 2019 ; Hu et al, 2018 ). Exactly how this symmetry mismatch might be overcome remains unclear, but there is mounting evidence to suggest the overall stoichiometry of the secretin may fluctuate to be compatible with the stoichiometry of its IM partner (Barbat et al, 2023 ; Hay et al, 2017 ). In principle the same could occur for PqiC, however, this seems somewhat less likely due to the coinciding diameters of the hexameric PqiB coiled-coil and octameric PqiC pore.…”

Section: Discussionmentioning

confidence: 99%

An octameric PqiC toroid stabilises the outer-membrane interaction of the PqiABC transport system

Cooper,

Ratkevičiūtė,

Clifton

et al. 2024

EMBO Rep

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The E. coli Paraquat Inducible (Pqi) Pathway is a putative Gram-negative phospholipid transport system. The pathway comprises three components: an integral inner membrane protein (PqiA), a periplasmic spanning MCE family protein (PqiB) and an outer membrane lipoprotein (PqiC). Interactions between all complex components, including stoichiometry, remain uncharacterised; nevertheless, once assembled into their quaternary complex, the trio of Pqi proteins are anticipated to provide a continuous channel between the inner and outer membranes of diderms. Here, we present X-ray structures of both the native and a truncated, soluble construct of the PqiC lipoprotein, providing insight into its biological assembly, and utilise neutron reflectometry to characterise the nature of the PqiB-PqiC-membrane interaction. Finally, we employ phenotypic complementation assays to probe specific PqiC residues, which imply the interaction between PqiB and PqiC is less intimate than previously anticipated.

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“…10H ). Furthermore, the 3:6 association of PulF with the ATPase makes the trimer the common element of the stoichiometry puzzle in the T2SS machinery, from the hexameric ATPase at the IM to the pentadecameric secretin in the outer membrane ( 49 , 61 – 63 ). By analogy, the same 6:3 stoichiometry is expected to exist in T4P for the PilB/T:PilC complex.…”

Section: Discussionmentioning

confidence: 99%

Membrane platform protein PulF of the Klebsiella type II secretion system forms a trimeric ion channel essential for endopilus assembly and protein secretion

Guilvout,

Samsudin,

Huber

et al. 2024

mBio

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Type IV pili and type II secretion systems (T2SS) are crucial for bacterial adaptation, virulence, and environmental impact. A common mechanism underlying their multiple functions involves assembly of dynamic plasma membrane-anchored filaments—the (endo)pili. The cytoplasmic ATPase motor GspE/PilB is thought to energize pilus assembly via the membrane assembly platform protein GspF/PilC, but platform protein structure and its molecular role remain elusive. Here, to dissect the GspF/PilC architecture and mechanism, we generated all-atom models of the Klebsiella T2SS platform protein PulF in different oligomeric states. Comprehensive modeling, molecular dynamics (MD) simulations, cysteine crosslinking, and biochemical analyses support the trimeric state of PulF. In the trimer, the transmembrane segment TMS2 and the nonessential cytoplasmic N-domain are peripherally located, while TMS1 and TMS3 form a 6-helix bundle delineating a central transmembrane channel. Polar and proline residue pairs in these segments, conserved in all GspF/PilC homologs, define the channel constriction that can accommodate sodium ions or protons. Remarkably, obstructing this channel via Cys crosslinking abolished endopilus assembly and protein secretion, shedding light on previous findings showing that dissipating the membrane potential with ionophores reversibly abolished T2SS function. The trimeric PulF shows an excellent fit with the PulE ATPase hexamer, building a complex with structural similarities to the V-ATPase. MD simulations of PulF inserted in an Escherichia coli membrane model reveal strong binding and enrichment in cardiolipin, the phospholipid known to stimulate ATPase activity of GspE/PilB. We propose that GspF/PilC cooperates with the ATPase to energize (endo)pilus assembly using the ion motive force. IMPORTANCE Type IV pili and type II secretion systems are members of the widespread type IV filament (T4F) superfamily of nanomachines that assemble dynamic and versatile surface fibers in archaea and bacteria. The assembly and retraction of T4 filaments with diverse surface properties and functions require the plasma membrane platform proteins of the GspF/PilC superfamily. Generally considered dimeric, platform proteins are thought to function as passive transmitters of the mechanical energy generated by the ATPase motor, to somehow promote insertion of pilin subunits into the nascent pilus fibers. Here, we generate and experimentally validate structural predictions that support the trimeric state of a platform protein PulF from a type II secretion system. The PulF trimers form selective proton or sodium channels which might energize pilus assembly using the membrane potential. The conservation of the channel sequence and structural features implies a common mechanism for all T4F assembly systems. We propose a model of the oligomeric PulF—PulE ATPase complex that provides an essential framework to investigate and understand the pilus assembly mechanism.

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Structural lessons on bacterial secretins

Cited by 6 publications

References 66 publications

Mechanism of assembly of type 4 filaments: everything you always wanted to know (but were afraid to ask)

Mechanism of assembly of type 4 filaments: everything you always wanted to know (but were afraid to ask)

An octameric PqiC toroid stabilises the outer-membrane interaction of the PqiABC transport system

Membrane platform protein PulF of the Klebsiella type II secretion system forms a trimeric ion channel essential for endopilus assembly and protein secretion

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