soc

Gene Description

Small outer capsid protein Soc (80 amino acids) is a nonessential decoration protein that binds to the exterior surface of the bacteriophage T4 capsid after proteolytic maturation and expansion of the major capsid protein (gp23*) lattice. Assembling as ~270-290 trimeric clamps (~810-870 monomers per wild-type prolate head, or 660 monomers in T=13 isometric heads) at the quasi-threefold interfaces between adjacent gp23* hexameric capsomers, Soc forms a continuous external cage that reinforces regions of high lattice curvature and stabilizes the DNA-filled capsid against extreme alkaline pH (above pH 10.6), osmotic shock, and elevated temperature.

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0019028 viral capsid	IEA GO_REF:0000120	MODIFY	Summary: Soc binds the outer surface of the expanded T4 capsid as a decoration clamp, which is more specifically represented by the descendant term GO:0098021 (viral capsid, decoration). Reason: GO:0019028 (viral capsid) is accurate but less specific than GO:0098021 (viral capsid, decoration), which is already present on this record. Proposed replacements: viral capsid, decoration Supporting Evidence: PMID:28893988 The capsid is further stabilized by Soc molecules, which form an external cage of 200 trimers, each clamping three adjacent capsomers. file:BPT4/soc/soc-uniprot.txt Capsid decoration protein which helps to stabilize the capsid against extremes of pH and temperature.
GO:0098021 viral capsid, decoration	IEA GO_REF:0000120	ACCEPT	Summary: Soc is an archetypal viral capsid decoration protein that clamps adjacent gp23* hexamers on the exterior of the mature T4 head. Reason: Structural and biochemical studies establish that Soc binds exclusively to the expanded outer capsid lattice as a reinforcing decoration clamp. Supporting Evidence: PMID:28893988 The capsid is further stabilized by Soc molecules, which form an external cage of 200 trimers, each clamping three adjacent capsomers. file:BPT4/soc/soc-deep-research-falcon.md Soc (small outer capsid protein) is a T4 head-shell accessory protein that decorates the exterior surface of the mature capsid and functions primarily as a structural clamp (“glue”) that reinforces the gp23* capsid lattice.
GO:0098021 viral capsid, decoration	IMP PMID:28893988 Cryo-EM structure of the bacteriophage T4 isometric head at ...	ACCEPT	Summary: 3.3 A cryo-EM structure in PMID:28893988 demonstrates that Soc trimers clamp adjacent gp23* hexamers across the outer capsid surface with highest occupancy around the high-strain fivefold vertices. Reason: Near-atomic cryo-EM reconstruction directly resolves the external cage of Soc decoration clamps bridging neighboring gp23* hexameric capsomers. Supporting Evidence: PMID:28893988 The capsid is further stabilized by Soc molecules, which form an external cage of 200 trimers, each clamping three adjacent capsomers.
GO:0039660 structural constituent of virion	NAS PMID:28893988 Cryo-EM structure of the bacteriophage T4 isometric head at ...	NEW	Summary: Soc is a high-copy structural component (~810-870 copies per prolate head) of the mature T4 capsid exterior that mechanically clamps adjacent gp23* hexamers. Reason: Soc forms a structural external cage on the mature virion capsid that reinforces inter-capsomer interfaces against internal DNA pressure and alkaline pH. Supporting Evidence: PMID:28893988 The capsid is further stabilized by Soc molecules, which form an external cage of 200 trimers, each clamping three adjacent capsomers. file:BPT4/soc/soc-uniprot.txt Capsid decoration protein which helps to stabilize the capsid against extremes of pH and temperature.

Core Functions

Binds as trimeric clamps across the quasi-threefold interfaces between adjacent gp23* hexameric capsomers on the exterior of the expanded capsid, forming an external decoration cage that stabilizes the virion head against extreme pH and temperature.

Molecular Function:

structural constituent of virion

Supporting Evidence:

PMID:28893988
The capsid is further stabilized by Soc molecules, which form an external cage of 200 trimers, each clamping three adjacent capsomers.
file:BPT4/soc/soc-uniprot.txt
Capsid decoration protein which helps to stabilize the capsid against extremes of pH and temperature.
file:BPT4/soc/soc-deep-research-falcon.md
**Soc (small outer capsid protein)** is a T4 head-shell accessory protein that **decorates the exterior surface** of the mature capsid and functions primarily as a **structural clamp (“glue”)** that reinforces the gp23* capsid lattice.

References

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Suggested Experiments

Experiment: Perform atomic force microscopy (AFM) nanoindentation and differential scanning calorimetry on soc-deficient T4 capsids titrated with wild-type Soc versus C-terminal trimerization-interface mutants to separate the mechanical contributions of monomer bridging from trimeric clamping.

Experiment: Measure single-molecule binding kinetics of fluorescently labeled Soc to immobilized isometric (T=13) versus prolate (Tend=13, Tmid=20) soc-minus capsids across a range of pH and ionic strengths using total internal reflection fluorescence (TIRF) microscopy.

Gene Description

Existing Annotations Review

Core Functions

Binds as trimeric clamps across the quasi-threefold interfaces between adjacent gp23* hexameric capsomers on the exterior of the expanded capsid, forming an external decoration cage that stabilizes the virion head against extreme pH and temperature.

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

📚 Additional Documentation

Notes

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