vgrG1a (PA0091, Q9I741) notes

Review session 2026-11-05 (PseudoCAP IBA-seed protocol, tier 2)

Fetched with just fetch-gene PSEAE Q9I741 --alias vgrG1a; accession matches the
worklist (reviewed entry VGR1A_PSEAE). No deep-research provider key was
available. Cached full texts: PMID:20114026, PMID:21325275, PMID:24794869,
PMID:30177742. Abstract only: PMID:16763151, PMID:26894531, PMID:30455305
(the last three fetched with just fetch-pmid).

Identity and literature

643 aa VgrG-family spike protein, encoded in HSI-I (the H1-T6SS cluster).
Trimeric needle structure solved at 2.0 A
PMID:26894531.
Secreted in a ClpV1-dependent manner, unlike VgrG1b
PMID:21325275.
Required, redundantly with VgrG1c, for Hcp1 export
PMID:21325275;
the double deletion abolishes Hcp1 secretion while deletion of the Tse cargo
proteins does not
PMID:20114026.
Note the older nomenclature: vgrG1 = vgrG1a (PA0091), vgrG4 = vgrG1c (PA2685).
VgrGs are also needed for export of other substrates
PMID:21325275,
and each VgrG pairs with its own cargo
PMID:24794869.
Cargo loading onto VgrG1a needs the chaperone EagT6 (UniProt SUBUNIT, from
PMID:30177742).

PseudoCAP IBA-seed assessment

PTN node	node term	n_seeds	leaf IBAs	seed annotation (term, evidence, PMID)	verdict	rationale	other seeds	IBD stands without this seed?
PTN002088178	GO:0033103 protein secretion by the type VI secretion system	3 (Q9I741, Q9I0F3, Q9I737)	13 (3 taxa)	GO:0033103, IDA PMID:20114026 and IMP PMID:21325275 (PseudoCAP)	SOUND	The protein is exported by the H1-T6SS and is required, with VgrG1c, for Hcp1 export; both papers read in full.	vgrG1c (Q9I0F3), equally sound; vgrG1b (Q9I737), WRONG reference (see genes/PSEAE/vgrG1b)	Yes
PTN002088178	GO:0033104 type VI protein secretion system complex	3 (Q9I741, Q9I0F3, Q9I737)	13 (3 taxa)	GO:0033104, IDA PMID:20114026 and IMP PMID:21325275 (PseudoCAP)	SOUND	VgrG1a is the spike at the tip of the Hcp1 tube (crystal structure), and behaves as an apparatus component rather than cargo.	as above	Yes

The node is small and tight: the 13 leaves are P. aeruginosa VgrGs (vgrG1a,
vgrG1b, vgrG1c, vgrG4b, vgrG5, PA2373, PA3294, PA5266) plus Yersinia pestis and
Salmonella homologues, so the node terms suit the clade. No GO_CENTRAL defect
is warranted: the IBDs stand on the vgrG1a and vgrG1c seeds even after the
vgrG1b reference problem is set aside.

Decisions summary

ACCEPT: GO:0033103 (IBA, IDA, IEA, IGC, IMP), GO:0033104 (IBA, IDA, IEA, IGC,
IMP).
KEEP_AS_NON_CORE: extracellular region (EXP, IEA) — a consequence of firing.
Counts: ACCEPT 10, KEEP_AS_NON_CORE 2.
Defects: none for this gene (PSEUDOCAP 0, GO_CENTRAL 0).