Long-tail fiber protein gp35 (372 amino acids) is the monomeric hinge ("kneecap") subunit of the bacteriophage T4 long tail fiber ((gp34)3(gp35)1(gp36)3(gp37)3). During distal half-fiber morphogenesis, a single molecule of gp35 binds asymmetrically to the N-terminal tip of the homotrimeric gp36-gp37 subassembly and provides the specific docking interface for the C-terminal end of the homotrimeric gp34 proximal half-fiber, forming the characteristic angled knee joint of the mature long tail fiber and mechanically coupling distal receptor binding to baseplate activation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0019062 virion attachment to host cell | IEA GO_REF:0000043 | MODIFY | Summary: gp35 is a structural subunit of the long tail fiber apparatus that mediates reversible adhesion-receptor attachment to the host cell (GO:0098671). Reason: GO:0019062 is a broader parent of GO:0098671 (adhesion receptor-mediated virion attachment to host cell), which is already present on this record. Proposed replacements: adhesion receptor-mediated virion attachment to host cell Supporting Evidence: file:BPT4/35/35-uniprot.txt Structural component of the distal-half of the long-tail fiber. The long-tail fiber of T4 is about 1600 Angstroms long with a kink in the middle that divides the fiber into proximal and distal halves. The latter hinge is probably composed of gp35 protein. |
| GO:0030246 carbohydrate binding | IEA GO_REF:0000043 | REMOVE | Summary: Electronic inference from the PROSITE GG-lectin domain profile (PS51918); structural and functional studies indicate that the CBM-like beta-jellyroll folds of gp35 mediate protein-protein interactions with the gp36 and gp34 trimers at the fiber hinge rather than binding host carbohydrates. Reason: In the T4 long tail fiber, host LPS/OmpC receptor binding is performed by the distal tip of gp37, whereas the CBM/lectin-like folds of gp35 are repurposed as an asymmetric structural adapter connecting the homotrimeric gp36 and gp34 half-fibers at the knee joint. Supporting Evidence: file:BPT4/35/35-uniprot.txt Structural component of the distal-half of the long-tail fiber. The long-tail fiber of T4 is about 1600 Angstroms long with a kink in the middle that divides the fiber into proximal and distal halves. The latter hinge is probably composed of gp35 protein. file:BPT4/35/35-deep-research-falcon.md Gene 35 of *Enterobacteria phage T4* encodes gp35, a **monomeric hinge (“kneecap”) structural protein** of the phage **long tail fiber (LTF)**. |
| GO:0046718 symbiont entry into host cell | IEA GO_REF:0000043 | MODIFY | Summary: Overly broad keyword-derived term; as part of the long tail fiber, gp35 participates in reversible adhesion receptor-mediated virion attachment (GO:0098671) prior to tail contraction and genome ejection. Reason: The long tail fiber functions in initial receptor-mediated host attachment (GO:0098671) rather than membrane penetration or genome entry itself. Proposed replacements: adhesion receptor-mediated virion attachment to host cell Supporting Evidence: file:BPT4/35/35-uniprot.txt Structural component of the distal-half of the long-tail fiber. The long-tail fiber of T4 is about 1600 Angstroms long with a kink in the middle that divides the fiber into proximal and distal halves. The latter hinge is probably composed of gp35 protein. |
| GO:0098015 virus tail | IEA GO_REF:0000043 | MODIFY | Summary: gp35 localizes specifically to the long tail fiber (GO:0098024), where it forms the central hinge ("kneecap") between the proximal and distal half-fibers. Reason: GO:0098015 (virus tail) is less specific than its child term GO:0098024 (virus tail, fiber), which is already present on this record. Proposed replacements: virus tail, fiber Supporting Evidence: file:BPT4/35/35-uniprot.txt Structural component of the distal-half of the long-tail fiber. The long-tail fiber of T4 is about 1600 Angstroms long with a kink in the middle that divides the fiber into proximal and distal halves. The latter hinge is probably composed of gp35 protein. |
| GO:0098024 virus tail, fiber | IEA GO_REF:0000043 | ACCEPT | Summary: gp35 is an integral structural polypeptide of the T4 long tail fiber, forming the monomeric knee hinge connecting the gp34 proximal and gp36-gp37 distal half-fibers. Reason: Biochemical, genetic, and EM studies establish that each long tail fiber contains one monomer of gp35 at the hinge joint between the proximal and distal half-fibers. Supporting Evidence: file:BPT4/35/35-uniprot.txt Structural component of the distal-half of the long-tail fiber. The long-tail fiber of T4 is about 1600 Angstroms long with a kink in the middle that divides the fiber into proximal and distal halves. The latter hinge is probably composed of gp35 protein. file:BPT4/35/35-deep-research-falcon.md Gene 35 of *Enterobacteria phage T4* encodes gp35, a **monomeric hinge (“kneecap”) structural protein** of the phage **long tail fiber (LTF)**. |
| GO:0098671 adhesion receptor-mediated virion attachment to host cell | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: While the distal tip of gp37 directly binds host LPS and OmpC receptors, gp35 forms the hinge connecting the distal and proximal half-fibers and is required to assemble functional long tail fibers that mediate host attachment. Reason: gp35 does not directly contact the bacterial receptor (which is bound by gp37), but as the structural hinge of the long tail fiber it mechanically transmits the receptor-binding signal to the proximal half-fiber and baseplate. Supporting Evidence: file:BPT4/35/35-uniprot.txt Structural component of the distal-half of the long-tail fiber. The long-tail fiber of T4 is about 1600 Angstroms long with a kink in the middle that divides the fiber into proximal and distal halves. The latter hinge is probably composed of gp35 protein. |
| GO:0039660 structural constituent of virion | NAS file:BPT4/35/35-deep-research-falcon.md | NEW | Summary: gp35 is an essential structural subunit of the mature T4 virion, forming the monomeric kneecap hinge of each of the six long tail fibers. Reason: Six copies of gp35 (one per long tail fiber) are permanently incorporated into the mature T4 virion as the hinge connector between gp34 and gp36. Supporting Evidence: file:BPT4/35/35-uniprot.txt Structural component of the distal-half of the long-tail fiber. The long-tail fiber of T4 is about 1600 Angstroms long with a kink in the middle that divides the fiber into proximal and distal halves. The latter hinge is probably composed of gp35 protein. file:BPT4/35/35-deep-research-falcon.md Gene 35 of *Enterobacteria phage T4* encodes gp35, a **monomeric hinge (“kneecap”) structural protein** of the phage **long tail fiber (LTF)**. |
| GO:0098004 virus tail fiber assembly | NAS file:BPT4/35/35-deep-research-falcon.md | NEW | Summary: Capping of the N-terminus of the gp36-gp37 distal half-fiber intermediate by a single gp35 monomer is a mandatory step in long tail fiber assembly that enables subsequent joining to the gp34 proximal half-fiber. Reason: Without gp35 binding to the gp36-gp37 complex, the distal and proximal half-fibers cannot join to form complete long tail fibers. Supporting Evidence: file:BPT4/35/35-uniprot.txt Structural component of the distal-half of the long-tail fiber. The long-tail fiber of T4 is about 1600 Angstroms long with a kink in the middle that divides the fiber into proximal and distal halves. The latter hinge is probably composed of gp35 protein. file:BPT4/35/35-deep-research-falcon.md Gene 35 of *Enterobacteria phage T4* encodes gp35, a **monomeric hinge (“kneecap”) structural protein** of the phage **long tail fiber (LTF)**. |
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Download this section (compressed HTML)Q: How does a single asymmetric monomer of gp35 simultaneously accommodate the three-fold symmetry of the N-terminal gp36 trimer and the C-terminal gp34 trimer while imposing a fixed hinge angle at the long tail fiber knee?
Q: Does the hinge angle of gp35 flex elastically during reversible host scanning, and how does interaction with the fibritin (gpwac) whiskers at the knee stabilize the retracted long tail fiber conformation?
Experiment: Determine the X-ray crystal or cryo-EM structure of a reconstituted gp34(C-terminal trimer)-gp35(monomer)-gp36(N-terminal trimer) hinge complex to resolve the symmetry-mismatch interfaces and the structural basis of the knee bend.
Experiment: Perform glycan microarray screening with purified recombinant gp35 and the gp35-gp36-gp37 distal half-fiber to confirm experimentally that the CBM-like domains of gp35 lack autonomous carbohydrate-binding activity.
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