Dual Targeting Factors Are Required for LXG Toxin Export by the Bacterial Type VIIb Secretion System

Klein, Timothy A.; Grebenc, Dirk W.; Shah, Prakhar Y; McArthur, Owen D.; Dickson, Brandon H; Surette, Michael G.; Kim, Young Chang; Whitney, John C.

doi:10.1128/mbio.02137-22

Cited by 22 publications

(69 citation statements)

References 79 publications

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“…2A, Supp. Table 1 ), similar to those described in S. intermedius (Klein et al ., 2022). GBS Lap2 proteins are not well conserved across subtypes I-III, with ≤41% identity between any two ( Supp.…”

Section: Resultssupporting

confidence: 86%

“…1C). A similar gene cluster was recently described in S. intermedius where the DUF3130 gene and the adjacent gene encode accessory proteins/chaperones required for secretion of the LXG toxins TelC and TelD (Klein et al, 2022). Consequently, these chaperones were named LXG-associated α-helical proteins (Lap).…”

Section: Putative T7ss Effectors Chaperones and Immunity Factorsmentioning

confidence: 82%

“…In S. aureus , two WXG-like proteins named EsxC and EsxD can heterodimerize with EsxA and EsxB, respectively, and substrate secretion is interdependent as deletion of these WXG-like genes impacts EsxA/B export (Anderson et al ., 2013). In S. intermedius , WXG-like genes adjacent to essC facilitate secretion of a downstream LXG toxin (Klein et al ., 2022). We have observed that a double mutant in both these WXG-like genes in GBS subtype I did not affect EsxA secretion (data not shown); therefore, we hypothesize that GBS WXG-like proteins may function in LXG protein secretion, similar to S. intermedius .…”

Section: Discussionmentioning

confidence: 99%

“…Transmembrane protein and DUF4176 protein encoding genes, commonly observed in the vicinity of T7SS loci and toxins, appeared downstream of the LXG genes in GBS subtypes I-III. In S. aureus , cognate immunity factor esaG (DUF600) is encoded downstream of nuclease EsaD (Cao et al ., 2016) and in S. intermedius , Tel immunity proteins are encoded either adjacent to (in the case of TelB, TelC, TelD) or one gene separated (in the case of TelA) from the LXG toxin (Whitney et al ., 2017, Klein et al ., 2022). We therefore expect that one of these downstream GBS genes encodes a subtype specific immunity factor and determining these LXG toxin-immunity factor pairs is the subject of our future work.…”

Section: Discussionmentioning

confidence: 99%

“…Some T7SS toxins function in interbacterial competition and are frequently co-transcribed with chaperones that facilitate their secretion and immunity factors that prevent self-toxicity. These functions have been described in Staphylococcus aureus, Streptococcus intermedius, Bacillus subtilis, Enterococcus faecalis , and recently Streptococcus gallolyticus (Cao et al ., 2016, Whitney et al ., 2017, Klein et al ., 2018, Ulhuq et al ., 2020, Kobayashi, 2021, Chatterjee et al ., 2021, Teh et al ., 2022, Klein et al ., 2022). Interestingly, in some cases, these toxins also promote virulence and modulate immune responses within the host (Dai et al ., 2017, Ohr et al ., 2017, Ulhuq et al ., 2020).…”

Section: Introductionmentioning

confidence: 99%

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Heterogeneity of the group B streptococcal type VII secretion system and influence on colonization of the female genital tract

Spencer

Job

Robertson

et al. 2023

Preprint

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Type VIIb secretion systems (T7SSb) in Gram-positive bacteria facilitate physiology, interbacterial competition, and/or virulence via EssC ATPase-driven secretion of small ɑ-helical proteins and toxins. Recently, we characterized T7SSb in group B Streptococcus (GBS), a leading cause of infection in newborns and immunocompromised adults. GBS T7SS comprises four subtypes based on variation in the C-terminus of EssC and the repertoire of downstream effectors; however, the intra-species diversity of GBS T7SS and impact on GBS-host interactions remains unknown. Bioinformatic analysis indicates that GBS T7SS loci encode subtype-specific putative effectors, which have low inter-species and inter-subtype homology but contain similar domains/motifs and therefore may serve similar functions. We further identify orphaned GBS WXG100 proteins. Functionally, we show that GBS T7SS subtype I and III strains secrete EsxA in vitro and that in subtype I strain CJB111, esxA1 appears to be differentially transcribed from the T7SS operon. Further, we observe subtype-specific effects of GBS T7SS on host colonization, as subtype I but not subtype III T7SS promotes GBS vaginal persistence. Finally, we observe that T7SS subtypes I and II are the predominant subtypes in clinical GBS isolates. This study highlights the potential impact of T7SS heterogeneity on host-GBS interactions.

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Section: Resultssupporting

confidence: 86%

Section: Putative T7ss Effectors Chaperones and Immunity Factorsmentioning

confidence: 82%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Heterogeneity of the group B streptococcal type VII secretion system and influence on colonization of the female genital tract

Spencer

Job

Robertson

et al. 2023

Preprint

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A type VII-secreted lipase toxin with reverse domain arrangement

Garrett,

Mietrach,

Deme

et al. 2023

Nat Commun

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The type VII protein secretion system (T7SS) is found in many Gram-positive bacteria and in pathogenic mycobacteria. All T7SS substrate proteins described to date share a common helical domain architecture at the N-terminus that typically interacts with other helical partner proteins, forming a composite signal sequence for targeting to the T7SS. The C-terminal domains are functionally diverse and in Gram-positive bacteria such as Staphylococcus aureus often specify toxic anti-bacterial activity. Here we describe the first example of a class of T7 substrate, TslA, that has a reverse domain organisation. TslA is widely found across Bacillota including Staphylococcus, Enterococcus and Listeria. We show that the S. aureus TslA N-terminal domain is a phospholipase A with anti-staphylococcal activity that is neutralised by the immunity lipoprotein TilA. Two small helical partner proteins, TlaA1 and TlaA2 are essential for T7-dependent secretion of TslA and at least one of these interacts with the TslA C-terminal domain to form a helical stack. Cryo-EM analysis of purified TslA complexes indicate that they share structural similarity with canonical T7 substrates. Our findings suggest that the T7SS has the capacity to recognise a secretion signal present at either end of a substrate.

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Structure of a tripartite protein complex that targets toxins to the type VII secretion system

Klein,

Shah,

Gkragkopoulou

et al. 2024

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

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Type VII secretion systems are membrane-embedded nanomachines used by Gram-positive bacteria to export effector proteins from the cytoplasm to the extracellular environment. Many of these effectors are polymorphic toxins comprised of an N-terminal Leu-x-Gly (LXG) domain of unknown function and a C-terminal toxin domain that inhibits the growth of bacterial competitors. In recent work, it was shown that LXG effectors require two cognate Lap proteins for T7SS-dependent export. Here, we present the 2.6 Å structure of the LXG domain of the TelA toxin from the opportunistic pathogen Streptococcus intermedius in complex with both of its cognate Lap targeting factors. The structure reveals an elongated α-helical bundle within which each Lap protein makes extensive hydrophobic contacts with either end of the LXG domain. Remarkably, despite low overall sequence identity, we identify striking structural similarity between our LXG complex and PE–PPE heterodimers exported by the distantly related ESX type VII secretion systems of Mycobacteria implying a conserved mechanism of effector export among diverse Gram-positive bacteria. Overall, our findings demonstrate that LXG domains, in conjunction with their cognate Lap targeting factors, represent a tripartite secretion signal for a widespread family of T7SS toxins.

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Dual Targeting Factors Are Required for LXG Toxin Export by the Bacterial Type VIIb Secretion System

Cited by 22 publications

References 79 publications

Heterogeneity of the group B streptococcal type VII secretion system and influence on colonization of the female genital tract

Heterogeneity of the group B streptococcal type VII secretion system and influence on colonization of the female genital tract

A type VII-secreted lipase toxin with reverse domain arrangement

Structure of a tripartite protein complex that targets toxins to the type VII secretion system

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