VgrG1a (PA0091) is a valine-glycine repeat G (VgrG) spike protein of the H1 type VI secretion system (H1-T6SS) of Pseudomonas aeruginosa, encoded within the HSI-I cluster. It forms a homotrimeric needle-like spike, structurally related to the gp27/gp5 puncturing complex of phage T4, that caps the Hcp1 tube, and it is itself exported by the H1-T6SS in a ClpV1-dependent manner. VgrG1a, or the paralogous VgrG1c, is required for Hcp1 secretion, and VgrG proteins are also needed for export of H1-T6SS substrates. VgrG1a serves as the carrier for a specific subset of H1-T6SS cargo proteins, which it loads with the help of the chaperone EagT6.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005576 extracellular region | EXP PMID:21325275 Type VI secretion system in Pseudomonas aeruginosa: secretio... | KEEP AS NON CORE | Summary: VgrG1a is recovered from culture supernatants in a ClpV1-dependent manner. Reason: Correct, but peripheral. The spike is exported when the system fires, so it appears outside the cell; where it does its work is the assembled apparatus. Supporting Evidence: PMID:21325275 Whereas VgrG1a and VgrG1c were secreted in a ClpV1-dependent manner, secretion of VgrG1b was ClpV1-independent. |
| GO:0005576 extracellular region | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: Combined IEA (ARBA plus the UniProt "Secreted" subcellular location). Reason: Same claim as the EXP row, which shows it directly; non-core for the same reason. Supporting Evidence: PMID:20114026 These data show that the H1-T6SS exports at least two VgrG-family proteins. |
| GO:0033103 protein secretion by the type VI secretion system | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN002088178 (a VgrG clade, 13 leaf IBAs in P. aeruginosa, Yersinia pestis and Salmonella), seeded by the PseudoCAP rows on VgrG1a, VgrG1b and VgrG1c. Reason: Core process. The IDA and IMP seeds on this protein are sound, so its appearance in WITH/FROM is the expected mark of experimental grounding on the target. The node term suits a clade of T6SS spike proteins. Supporting Evidence: PMID:21325275 In conclusion, VgrG1a and VgrG1c are essential for efficient Hcp1 secretion but can function independently. |
| GO:0033103 protein secretion by the type VI secretion system | IDA PMID:20114026 A type VI secretion system of Pseudomonas aeruginosa targets... | ACCEPT | Summary: Hood et al. 2010: PA0091 is among the most abundant proteins of the on-state H1-T6SS secretome, its export needs ClpV1, and a PA0091 PA2685 double deletion abolishes Hcp1 secretion. Reason: Sound seed. The protein is both exported by the system and required for Hcp1 export, so it does part of the work of T6SS secretion. Supporting Evidence: PMID:20114026 Western blot analysis revealed that Hcp1 secretion was abolished in both the ΞclpV1 and ΞvgrG1 ΞvgrG4 strains, however it was unaffected by tse deletion |
| GO:0033103 protein secretion by the type VI secretion system | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA prediction of the same process. Reason: Same claim as the experimental rows, which establish it. Supporting Evidence: PMID:21325275 In conclusion, VgrG1a and VgrG1c are essential for efficient Hcp1 secretion but can function independently. |
| GO:0033103 protein secretion by the type VI secretion system | IGC PMID:16763151 A virulence locus of Pseudomonas aeruginosa encodes a protei... | ACCEPT | Summary: Mougous et al. 2006: the HSI-I locus, which contains PA0091, encodes a protein secretion apparatus that exports Hcp1. Reason: Genomic-context evidence (abstract only), confirmed by the later direct experiments on this protein. Supporting Evidence: PMID:16763151 Here we found that a virulence locus (HSI-I) of Pseudomonas aeruginosa encodes a protein secretion apparatus. |
| GO:0033103 protein secretion by the type VI secretion system | IMP PMID:21325275 Type VI secretion system in Pseudomonas aeruginosa: secretio... | ACCEPT | Summary: Hachani et al. 2011: the single vgrG1a deletion leaves residual secretion; with vgrG1c also deleted, Hcp1 secretion is abolished. Reason: Sound seed (full text read). VgrG1a and VgrG1c are redundant for Hcp1 export, and VgrG proteins are needed for export of other substrates. Supporting Evidence: PMID:21325275 However, when the vgrG1a mutation was combined with the vgrG1c mutation, Hcp1 secretion was abolished PMID:21325275 Our results demonstrate that VgrG proteins are not only secreted components but are essential for secretion of other T6SS substrates. |
| GO:0033104 type VI protein secretion system complex | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN002088178, seeded by VgrG1a, VgrG1b and VgrG1c. Reason: Core complex. The crystal structure shows the VgrG1a trimer is the spike at the tip of the Hcp1 tube, and the node term suits a VgrG clade. Supporting Evidence: PMID:26894531 Valine-glycine repeat protein G1 (VgrG1) forms the spike at the tip of the elongating tube formed by haemolysin co-regulated protein 1 (Hcp1) |
| GO:0033104 type VI protein secretion system complex | IDA PMID:20114026 A type VI secretion system of Pseudomonas aeruginosa targets... | ACCEPT | Summary: Hood et al. 2010: VgrGs, unlike the Tse cargo proteins, are required for Hcp1 export, so they behave as apparatus components. Reason: Sound seed; the structural work later confirmed VgrG1a is the tip of the apparatus. Supporting Evidence: PMID:20114026 In a systematic analysis, Hcp secretion was shown to require all predicted core T6SS components, including VgrG-family proteins |
| GO:0033104 type VI protein secretion system complex | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA prediction of complex membership. Reason: Same claim as the structural and experimental evidence. Supporting Evidence: PMID:26894531 Valine-glycine repeat protein G1 (VgrG1) forms the spike at the tip of the elongating tube formed by haemolysin co-regulated protein 1 (Hcp1) |
| GO:0033104 type VI protein secretion system complex | IGC PMID:16763151 A virulence locus of Pseudomonas aeruginosa encodes a protei... | ACCEPT | Summary: Genomic context; PA0091 lies in the HSI-I secretion-apparatus locus. Reason: Confirmed by the later direct and structural evidence. Supporting Evidence: PMID:16763151 Here we found that a virulence locus (HSI-I) of Pseudomonas aeruginosa encodes a protein secretion apparatus. |
| GO:0033104 type VI protein secretion system complex | IMP PMID:21325275 Type VI secretion system in Pseudomonas aeruginosa: secretio... | ACCEPT | Summary: Hachani et al. 2011: VgrG1a multimerises, co-purifies with Hcp1, and its loss (with vgrG1c) abolishes Hcp1 secretion. Reason: Sound seed for apparatus membership. Supporting Evidence: PMID:21325275 We show that VgrG1a and VgrG1c form multimers, which confirmed the VgrG model predicting trimers similar to the tail spike. |
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Download this section (compressed HTML)Q: What determines which cargo proteins associate with VgrG1a rather than with VgrG1c, given that the two are redundant for Hcp1 export?
Experiment: Swap the head domains of VgrG1a and VgrG1c in the chromosome and test, by secretion assays with tagged cargo, whether cargo specificity follows the head domain.
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