gp37 (1,026 amino acids, ~109.2 kDa) is the distal long tail fiber (LTF) subunit and primary host-range adhesin of bacteriophage T4. Assisted by the nonstructural molecular chaperones gp57A and gp38, three gp37 polypeptides fold into an elongated, heavily intertwined parallel fibrous homotrimer that forms the main shaft ("lower shin") and extreme C-terminal receptor-binding tip ("foot" or needle domain) of each of the six long tail fibers. The C-terminal tip contains paired histidine boxes (His-X-His motifs) that coordinate a row of seven octahedral Fe2+ ions along the trimer symmetry axis for structural stabilization and presents surface-exposed loops at the extreme apex that reversibly recognize and bind Escherichia coli outer membrane porin C (OmpC) and the inner core region of lipopolysaccharide (LPS).
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005198 structural molecule activity | IEA GO_REF:0000002 | MODIFY | Summary: gp37 is a structural subunit of the long tail fiber, so this broad InterPro-derived term should be refined to the virion-specific descendant GO:0039660 (structural constituent of virion). Reason: Three copies of gp37 form the distal shaft and receptor-binding tip of each of the six long tail fibers (18 copies per virion). GO:0005198 is true but overly general and is replaced by its direct virion-specific descendant GO:0039660 (structural constituent of virion). Proposed replacements: structural constituent of virion Supporting Evidence: file:BPT4/37/37-uniprot.txt Structural component of the distal-half of the long-tail |
| GO:0019062 virion attachment to host cell | IEA GO_REF:0000043 | MODIFY | Summary: gp37 directly mediates virion attachment to the host cell, and this general term should be refined to the more specific descendant GO:0098671 (adhesion receptor-mediated virion attachment to host cell) already present on this record. Reason: The C-terminal head domain of the gp37 trimer is the primary adhesin that recognizes host cell surface OmpC and LPS receptors. Because the more specific descendant term GO:0098671 (adhesion receptor-mediated virion attachment to host cell) is already annotated to gp37, GO:0019062 is modified to GO:0098671. Proposed replacements: adhesion receptor-mediated virion attachment to host cell Supporting Evidence: file:BPT4/37/37-uniprot.txt interacts with the bacterial lipopolysaccharide receptor and specifies |
| GO:0046718 symbiont entry into host cell | IEA GO_REF:0000043 | MODIFY | Summary: Broad automated mapping from the 'Viral attachment to host cell' keyword; gp37 specifically mediates initial reversible receptor recognition and attachment rather than viral penetration into the host cell. Reason: gp37 forms the distal tip of the external long tail fiber and mediates reversible adsorption to host surface LPS and OmpC; it does not cross the host envelope or directly catalyze cell envelope penetration. The annotation should be refined to GO:0098671 (adhesion receptor-mediated virion attachment to host cell). Proposed replacements: adhesion receptor-mediated virion attachment to host cell Supporting Evidence: file:BPT4/37/37-uniprot.txt interacts with the bacterial lipopolysaccharide receptor and specifies |
| GO:0098015 virus tail | IEA GO_REF:0000043 | MODIFY | Summary: gp37 localizes specifically to the long tail fiber, so the broader parent term virus tail should be refined to GO:0098024 (virus tail, fiber). Reason: gp37 forms the distal shaft and tip of the long tail fiber. Because the more specific descendant term GO:0098024 (virus tail, fiber) is already present on this record, GO:0098015 is modified to GO:0098024. Proposed replacements: virus tail, fiber Supporting Evidence: file:BPT4/37/37-uniprot.txt Structural component of the distal-half of the long-tail |
| GO:0098024 virus tail, fiber | IEA GO_REF:0000043 | ACCEPT | Summary: gp37 forms the main distal shaft and receptor-binding tip of the bacteriophage T4 long tail fiber. Reason: Structural, biochemical, and genetic studies demonstrate that the gp37 homotrimer constitutes the bulk of the ~70 nm distal half-fiber of the T4 long tail fiber. GO:0098024 accurately captures its core cellular component localization. Supporting Evidence: file:BPT4/37/37-uniprot.txt Structural component of the distal-half of the long-tail file:BPT4/37/37-deep-research-falcon.md T4 gp37 is a **virion structural protein** that forms the **distal half** of the bacteriophage T4 long tail fiber (LTF) and provides the **receptor-recognizing “foot/tip”** used for initial host contact. |
| GO:0098671 adhesion receptor-mediated virion attachment to host cell | IEA GO_REF:0000043 | ACCEPT | Summary: The C-terminal tip of the gp37 homotrimer is the primary adhesin of bacteriophage T4 that recognizes and binds host cell surface OmpC and LPS receptors. Reason: Unlike proximal tail fiber subunits, the C-terminal head domain of gp37 directly contacts host surface OmpC porin trimers and LPS inner-core glucosyl-alpha-1,3-glucose termini to mediate initial reversible phage adsorption and determine host range. GO:0098671 is a core biological process of gp37. Supporting Evidence: file:BPT4/37/37-uniprot.txt interacts with the bacterial lipopolysaccharide receptor and specifies file:BPT4/37/37-deep-research-falcon.md T4 gp37 is a **virion structural protein** that forms the **distal half** of the bacteriophage T4 long tail fiber (LTF) and provides the **receptor-recognizing “foot/tip”** used for initial host contact. |
| GO:0039660 structural constituent of virion | IEA file:BPT4/37/37-uniprot.txt | NEW | Summary: gp37 is an essential homotrimeric structural protein forming the distal shaft and tip of the mature T4 long tail fiber. Reason: To replace the overly broad GO:0005198 (structural molecule activity) annotation, GO:0039660 (structural constituent of virion) is added as the core molecular function of gp37 in forming the distal half-fiber shaft and tip of the mature virion. Supporting Evidence: file:BPT4/37/37-uniprot.txt Structural component of the distal-half of the long-tail file:BPT4/37/37-deep-research-falcon.md T4 gp37 is a **virion structural protein** that forms the **distal half** of the bacteriophage T4 long tail fiber (LTF) and provides the **receptor-recognizing “foot/tip”** used for initial host contact. |
| GO:0046872 metal ion binding | IEA file:BPT4/37/37-deep-research-falcon.md | NEW | Summary: The C-terminal needle domain of the gp37 homotrimer coordinates seven iron ions (Fe2+) along its central 3-fold axis via conserved His-X-His motifs. Reason: X-ray crystallography of the C-terminal tip fragment of gp37 (PDB 2XGF, 2.2 A) demonstrated that 14 histidine residues from each monomer (42 histidines per trimer arranged in paired His-X-His motifs) coordinate seven octahedral Fe2+ ions along the central axis of the intertwined trimer, stabilizing the receptor-binding needle structure. Supporting Evidence: file:BPT4/37/37-deep-research-falcon.md A striking feature of the needle is the presence of **multiple His–X–His motifs** coordinating **seven iron ions** along the fiber axis, likely stabilizing the fold and conferring mechanical rigidity needed for adsorption signaling. |
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Download this section (compressed HTML)Q: What is the high-resolution structure of the full-length gp37 shaft domains (residues 1-784) N-terminal to the crystallized C-terminal needle fragment (residues 785-1026), and how do they interface with the gp36 trimer?
Q: How do specific point mutations in the apical head domain loops of gp37 remodel the electrostatic and hydrogen-bonding network to switch receptor specificity between OmpC-dependent and LPS-only E. coli strains?
Experiment: Determine the cryo-EM structure of the gp37 distal tip bound to nanodisc-reconstituted Escherichia coli OmpC trimers and defined rough LPS oligosaccharides to resolve the atomic basis of dual-receptor recognition.
Experiment: Perform deep mutational scanning of the gp37 head domain (residues 932-996) across a panel of E. coli OmpC variants and LPS core chemotypes to map the complete sequence-to-receptor-specificity landscape.
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