Minor coat protein G7P (pVII, 33 residues), a single-pass hydrophobic peptide that forms a C5-symmetric pentameric plug at the apex of the distal (tail/round) tip of the filamentous bacteriophage M13 virion together with five copies of pIX. Prior to assembly, pVII inserts spontaneously into the Escherichia coli inner membrane. At the initiation of virion morphogenesis, pVII and pIX enter the inner-membrane pI/pXI assembly complex laterally and interact via their basic C-termini with the hairpin packaging signal of the progeny (+)ssDNA genome, nucleating the distal cap that emerges first from the bacterial host during concomitant virion assembly and extrusion.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0033644 host cell membrane | IEA GO_REF:0000044 | MODIFY | Summary: Broad host membrane annotation that should be refined to host cell plasma membrane (GO:0020002), where pVII is stored as a single-pass transmembrane protein prior to incorporation into the distal virion tip. Reason: Prior to virion assembly, pVII inserts into the bacterial host inner (plasma) membrane before entering the pI/pXI assembly complex to cap the emerging distal tip of the virion. Proposed replacements: host cell plasma membrane Supporting Evidence: file:BPM13/VII/VII-uniprot.txt Prior to assembly, is found associated with the bacterial host inner membrane. There are about five copies of this protein per mature phage that are located on the tail side of the filamentous virion with G9P (By similarity). |
| GO:0039660 structural constituent of virion | ISS file:BPM13/VII/VII-uniprot.txt | NEW | Summary: Five copies of pVII form a symmetric homopentameric plug at the apex of the distal ("round") tip of the mature M13 virion together with pIX. Reason: Cryo-EM reconstruction of the M13 distal tip (PubMed:37669979) shows that five subunits of pVII form a central pentameric plug capping the distal end of the virion. Supporting Evidence: file:BPM13/VII/VII-uniprot.txt Homopentamer (PubMed:37669979). G7P pentamer forms a symmetric plug-like structure located at the topmiddle of the virion tail round tip (PubMed:37669979). Interacts with G9P; this interaction allows integration of G7P and G9P into the virion tail round tip (PubMed:37669979). |
| GO:0019029 helical viral capsid | ISS file:BPM13/VII/VII-uniprot.txt | NEW | Summary: Five subunits of pVII are located with pIX at the distal (tail/round) tip of the mature M13 helical filamentous viral capsid. Reason: pVII is a minor capsid protein present in five copies at the distal tip of the mature M13 helical filamentous capsid. Supporting Evidence: file:BPM13/VII/VII-uniprot.txt Prior to assembly, is found associated with the bacterial host inner membrane. There are about five copies of this protein per mature phage that are located on the tail side of the filamentous virion with G9P (By similarity). |
| GO:0099045 viral extrusion | ISS file:BPM13/VII/VII-uniprot.txt | NEW | Summary: pVII and pIX interact with the viral (+)ssDNA packaging signal at the host inner membrane to initiate concomitant virion assembly and extrusion. Reason: Together with pIX, pVII recognizes the viral genome packaging signal at the host inner membrane and forms the distal cap that emerges first from the host cell during viral extrusion. Supporting Evidence: file:BPM13/VII/VII-uniprot.txt May initiate with G9P the virion concomitant assembly-budding process, by interacting with the packaging signal of the viral genome. The assembly-budding takes place at the host inner membrane. In turn, G7P and G9P are present at the end of the filamentous virion that emerges first from the bacterial host. |
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Download this section (compressed HTML)Q: How do the C-terminal Arg-33 residues of the pVII pentamer specifically recognize the stem-loop packaging signal hairpin of M13 (+)ssDNA within the pI/pXI inner-membrane assembly machine?
Q: Does pVII pre-assemble with pIX in the Escherichia coli inner membrane prior to entering the pI/pXI assembly complex, or are the two minor coat proteins recruited sequentially?
Experiment: Resolve the asymmetric cryo-EM reconstruction of the M13 distal tip (pVII-pIX pentamer) without imposing 5-fold symmetry to visualize specific contacts between pVII and the encapsulated (+)ssDNA packaging hairpin.
Experiment: Perform in vivo photo-crosslinking of amber-suppressed p-benzoyl-L-phenylalanine variants of pVII in E. coli to map its interaction surfaces with pIX, pI/pXI, and the packaging signal DNA during assembly initiation.
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