Structure of a periplasmic domain of the EpsAB fusion protein of the<i>Vibrio vulnificus</i>type II secretion system

Martynowski, Dariusz; Grochulski, P.; Howard, Peter

doi:10.1107/s0907444912042710

Cited by 10 publications

(7 citation statements)

References 29 publications

(29 reference statements)

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“…The induction of the Cpx response changes the expression of a set of genes that are enriched for inner membrane proteins, including a large group of transporter proteins, and also downregulates the production of envelope-spanning protein complexes involved in motility, secretion, and transport (11,32,51). In this light, it is interesting that a number of these complexes depend upon direct interactions with the peptidoglycan for assembly and function (52)(53)(54)(55). These observations may suggest that cell wall alterations could impact the activity and stability of secretion and transport complexes, potentially generating a Cpx-inducing signal.…”

Section: Discussionmentioning

confidence: 99%

The Cpx Envelope Stress Response Modifies Peptidoglycan Cross-Linking via the l,d-Transpeptidase LdtD and the Novel Protein YgaU

Bernal-Cabas¹,

Ayala²,

Raivio³

2014

J. Bacteriol.

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bThe Cpx envelope stress response mediates a complex adaptation to conditions that cause protein misfolding in the periplasm. A recent microarray study demonstrated that Cpx response activation led to changes in the expression of genes known, or predicted, to be involved in cell wall remodeling. We sought to characterize the changes that the cell wall undergoes during activation of the Cpx pathway in Escherichia coli. Luminescent reporters of gene expression confirmed that LdtD, a putative L,D-transpeptidase; YgaU, a protein of unknown function; and Slt, a lytic transglycosylase, are upregulated in response to Cpx-inducing conditions. Phosphorylated CpxR binds to the upstream regions of these genes, which contain putative CpxR binding sites, suggesting that regulation is direct. We show that the activation of the Cpx response causes an increase in the abundance of diaminopimelic acid (DAP)-DAP cross-links that involves LdtD and YgaU. Altogether, our data indicate that changes in peptidoglycan structure are part of the Cpx-mediated adaptation to envelope stress and indicate a role for the uncharacterized gene ygaU in regulating cross-linking. The envelope of Gram-negative bacteria is a complex multilayer structure that protects bacteria from changing conditions in the environment. This structure consists of the outer membrane, the inner membrane, and the periplasmic space. The periplasm contains the cell wall, which provides protection against osmotic stresses and maintains the cell shape. It also provides an oxidizing environment where periplasmic proteins that are translocated from the cytoplasm can be stabilized via disulfide bond formation (1). The periplasm is more sensitive to the conditions outside the cell than the cytoplasm due to the porous nature of the outer membrane (2). Consequently, bacteria have various stress responses whose function consists of sensing and responding to stresses in the periplasm. Among these, the sigma E and Cpx envelope stress responses are thought to respond to conditions that lead to misfolded outer membrane and periplasmic proteins, respectively (3-5, 66). Four additional pathways that respond to envelope stress have been described: the Bae (BaeSR), phage shock (Psp), Rcs, and vesicle release responses. The first three of these pathways have been linked to the efflux of toxic compounds, disruptions of proton motive force, and cell wall perturbations, respectively (6-8).Regulation of the Cpx pathway is carried out by the products of the cpxRA operon that encodes the response regulator CpxR and the histidine kinase CpxA. The Cpx pathway regulates numerous genes for periplasmic protein folding and degrading factors to alleviate envelope stress, including the protease/chaperone DegP, the disulfide oxidase DsbA, and the peptidyl-prolyl isomerase PpiA (9, 10). A recent microarray analysis (11) identified new members of the Cpx regulon by analyzing changes in gene expression after overexpression of NlpE (12), a well-known inducing cue of the Cpx pathway. Some of the novel genes ide...

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Section: Discussionmentioning

confidence: 99%

The Cpx Envelope Stress Response Modifies Peptidoglycan Cross-Linking via the l,d-Transpeptidase LdtD and the Novel Protein YgaU

Bernal-Cabas¹,

Ayala²,

Raivio³

2014

J. Bacteriol.

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“…However, in cross-complementation experiments, GspAB from V. cholerae restored secretin assembly and secretion in an A. hydrophila gspA mutant suggesting that GspAB performs the same role in Vibrio and Aeromonas. Supporting this idea that GspA and GspB act together, in Vibrio vulnificus they are naturally fused into a single polypeptide, the periplasmic portion of which possess a canonical peptidoglycan-binding domain [36]. However, in D. dadantii, K. oxytoca and some other bacteria, only GspB is present.…”

Section: Species Variationsmentioning

confidence: 99%

The role of intrinsic disorder and dynamics in the assembly and function of the type II secretion system

Shevchik

Shaw

et al. 2017

Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics

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Many Gram-negative commensal and pathogenic bacteria use a type II secretion system (T2SS) to transport proteins out of the cell. These exported proteins or substrates play a major role in toxin delivery, maintaining biofilms, replication in the host and subversion of host immune responses to infection. We review the current structural and functional work on this system and argue that intrinsically disordered regions and protein dynamics are central for assembly, exo-protein recognition, and secretion competence of the T2SS. The central role of intrinsic disorder-order transitions in these processes may be a particular feature of type II secretion.

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“…A GspS pilotin homolog is not found in the bacterium, and piloting and assembly of the ExeD secretin are dependent instead on the inner membrane complex ExeAB; in its absence, ExeD monomers accumulate in the inner membrane [24]. ExeA can be cross-linked to peptidoglycan in vivo , and genetic and structural analyses identified the location and critically important residues of its peptidoglycan-binding site [25–27]. Furthermore, the purified ExeA periplasmic domain forms large multimers in association with peptidoglycan in vitro [25].…”

Section: Introductionmentioning

confidence: 99%

Structure and assembly of pilotin-dependent and -independent secretins of the type II secretion system

Howard¹,

Estrozi²,

Bertrand³

et al. 2019

PLoS Pathog

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The type II secretion system (T2SS) is a cell envelope-spanning macromolecular complex that is prevalent in Gram-negative bacterial species. It serves as the predominant virulence mechanism of many bacteria including those of the emerging human pathogens Vibrio vulnificus and Aeromonas hydrophila . The system is composed of a core set of highly conserved proteins that assemble an inner membrane platform, a periplasmic pseudopilus and an outer membrane complex termed the secretin. Localization and assembly of secretins in the outer membrane requires recognition of secretin monomers by two different partner systems: an inner membrane accessory complex or a highly sequence-diverse outer membrane lipoprotein, termed the pilotin. In this study, we addressed the question of differential secretin assembly mechanisms by using cryo-electron microscopy to determine the structures of the secretins from A . hydrophila (pilotin-independent ExeD) and V . vulnificus (pilotin-dependent EpsD). These structures, at approximately 3.5 Å resolution, reveal pentadecameric stoichiometries and C-terminal regions that carry a signature motif in the case of a pilotin-dependent assembly mechanism. We solved the crystal structure of the V . vulnificus EpsS pilotin and confirmed the importance of the signature motif for pilotin-dependent secretin assembly by performing modelling with the C-terminus of EpsD. We also show that secretin assembly is essential for membrane integrity and toxin secretion in V . vulnificus and establish that EpsD requires the coordinated activity of both the accessory complex EpsAB and the pilotin EpsS for full assembly and T2SS function. In contrast, mutation of the region of the S-domain that is normally the site of pilotin interactions has little effect on assembly or function of the ExeD secretin. Since secretins are essential outer membrane channels present in a variety of secretion systems, these results provide a structural and functional basis for understanding the key assembly steps for different members of this vast pore-forming family of proteins.

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Structure of a periplasmic domain of the EpsAB fusion protein of theVibrio vulnificustype II secretion system

Cited by 10 publications

References 29 publications

The Cpx Envelope Stress Response Modifies Peptidoglycan Cross-Linking via the l,d-Transpeptidase LdtD and the Novel Protein YgaU

The Cpx Envelope Stress Response Modifies Peptidoglycan Cross-Linking via the l,d-Transpeptidase LdtD and the Novel Protein YgaU

The role of intrinsic disorder and dynamics in the assembly and function of the type II secretion system

Structure and assembly of pilotin-dependent and -independent secretins of the type II secretion system

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