Outer lipoprotein spanin subunit (o-spanin; PseT.2; gpY13J) is a 99-amino-acid precursor protein of bacteriophage T4 that is processed at its N-terminal signal peptidase II lipobox (cleaved after residue 16 and lipidated at Cys17) and anchored to the periplasmic leaflet of the Escherichia coli outer membrane. Together with its inner-membrane partner i-spanin (PseT.3 / Y13K), Y13J forms a periplasm-spanning two-component spanin complex that executes the final step of host cell lysis by disrupting the bacterial outer membraneโlikely via inner-to-outer membrane fusionโafter holin-mediated inner membrane permeabilization and endolysin-mediated peptidoglycan degradation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0020002 host cell plasma membrane | IEA GO_REF:0000044 | MODIFY | Summary: Inaccurate conservative mapping from UniProtKB-SubCell SL-0376 (Host cell outer membrane); in Gram-negative hosts, the o-spanin lipoprotein is anchored in the outer membrane rather than the plasma (inner) membrane. Reason: In Gram-negative bacteria such as Escherichia coli, the plasma membrane corresponds to the inner membrane (where the i-spanin partner y13K is anchored), whereas y13J (pseT.2) is an outer-membrane lipoprotein. Because GO lacks a dedicated host cell outer membrane term in this branch, GO:0033644 (host cell membrane) accurately encompasses its outer-membrane localization without conflating it with the plasma membrane. Proposed replacements: host cell membrane Supporting Evidence: file:BPT4/y13J/y13J-deep-research-falcon.md **Expected localization:** As an o-spanin, y13J/pseT.2 is expected to be an **outer membrane-anchored lipoprotein**, produced as a precursor and processed by signal peptidase II at the lipobox and lipidated at the N-terminal cysteine. file:BPT4/y13J/y13J-uniprot.txt SUBCELLULAR LOCATION: Host cell outer membrane {ECO:0000250}; Lipid-anchor {ECO:0000250}; Periplasmic side {ECO:0000250}. |
| GO:0031640 killing of cells of another organism | IEA GO_REF:0000043 | MODIFY | Summary: Broad keyword-derived term that should be refined to the specific descendant GO:0044659 (viral release from host cell by cytolysis) already annotated to the gene. Reason: Y13J specifically mediates the terminal outer-membrane disruption step of phage-induced host cytolysis for virion release, which is captured by the more specific descendant term GO:0044659 already present on this gene. Proposed replacements: viral release from host cell by cytolysis Supporting Evidence: PMID:17900620 In the case of T4, a deletion of a non-overlapping gene pair pseT.2 and pseT.3 identified as Rz/Rz1 equivalents resulted in the same divalent cation-dependent lysis phenotype. file:BPT4/y13J/y13J-deep-research-falcon.md **Best-supported function:** **o-spanin (outer membrane lipoprotein subunit) required for outer membrane disruption in lysis**, acting together with its partner i-spanin (pseT.3) as a **two-component spanin complex**. |
| GO:0044659 viral release from host cell by cytolysis | IGI PMID:17900620 Rz/Rz1 lysis gene equivalents in phages of Gram-negative hos... | ACCEPT | Summary: Directly supported by T4 deletion genetics demonstrating that the pseT.2/pseT.3 spanin pair is required for host outer membrane disruption and cell lysis. Reason: Summer et al. (2007) demonstrated that deletion of pseT.2 (y13J) and pseT.3 (y13K) in bacteriophage T4 causes a divalent cation-dependent lysis defect in which spherical cells fail to lyse and release progeny virions. Supporting Evidence: PMID:17900620 In the case of T4, a deletion of a non-overlapping gene pair pseT.2 and pseT.3 identified as Rz/Rz1 equivalents resulted in the same divalent cation-dependent lysis phenotype. file:BPT4/y13J/y13J-deep-research-falcon.md A constructed **ฮ(pseT.3 pseT.2)** mutant showed a classic spanin-null phenotype described as **Mg2+-dependent lysis defect** with infected cells adopting a **spherical morphology**โconsistent with successful PG degradation but failure to disrupt the OM barrier. |
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Download this section (compressed HTML)Q: Do the three conserved cysteines near the C-terminus of mature T4 Y13J form intermolecular disulfide bonds via the host DsbA/DsbC system analogous to phage lambda Rz1?
Q: What is the stoichiometry and structure of the periplasmic C-terminal heterocomplex between T4 Y13J (PseT.2) and Y13K (PseT.3) before and after peptidoglycan degradation?
Experiment: Perform non-reducing SDS-PAGE and site-directed mutagenesis of the cysteine residues in T4 Y13J (PseT.2) and Y13K (PseT.3) during T4 infection to test whether covalent disulfide-linked homodimerization is required for T4 spanin function.
Experiment: Reconstitute purified soluble periplasmic domains of T4 Y13J and Y13K into proteoliposomes to assay inner-outer membrane lipid mixing and determine the complex structure by cryo-EM.
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