gp57A (also known as gp57 or p57; 80 amino acids, ~8.6 kDa) is an essential, highly alpha-helical, nonstructural molecular chaperone of bacteriophage T4 required in the infected Escherichia coli cytoplasm for the folding and homotrimerization of three fibrous structural proteins: the short tail fiber subunit gp12, the proximal long tail fiber subunit gp34, and the distal long tail fiber subunit gp37 (the latter in concert with the gp37-specific chaperone gp38). Existing in solution as flexible alpha-helical oligomers linked to the inner cytoplasmic membrane, gp57A suppresses off-pathway aggregation of nascent fibrous polypeptides and promotes register-specific parallel trimerization without being incorporated into the mature virion.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0098003 viral tail assembly | IEA GO_REF:0000043 | MODIFY | Summary: gp57A specifically chaperones the folding and trimerization of the short and long tail fiber subunits (gp12, gp34, and gp37), so the broader parent term viral tail assembly should be refined to GO:0098004 (virus tail fiber assembly). Reason: gp57A acts exclusively in the assembly of the short tail fibers (gp12) and long tail fibers (gp34 and gp37) rather than the tail tube, sheath, or baseplate hub. Because the more specific descendant term GO:0098004 (virus tail fiber assembly) is already present on this record with experimental (IDA) and IEA support, GO:0098003 is modified to GO:0098004. Proposed replacements: virus tail fiber assembly Supporting Evidence: PMID:8892827 In the absence of the other, p57, p34 (another component of the long tail fiber), p37, and p12 (the subunit of the short tail fiber) remain unassembled. |
| GO:0098004 virus tail fiber assembly | IEA GO_REF:0000043 | ACCEPT | Summary: gp57A is an essential nonstructural chaperone required for the assembly of both short and long tail fibers in bacteriophage T4. Reason: In the absence of gp57A, the trimeric fibrous subunits of the short tail fiber (gp12) and the proximal (gp34) and distal (gp37) long tail fibers fail to fold and oligomerize into functional tail fibers. GO:0098004 accurately captures this core biological process. Supporting Evidence: file:BPT4/57/57-uniprot.txt Chaperone essential for folding and oligomerization of both file:BPT4/57/57-deep-research-falcon.md Gene **57** of *Enterobacteria phage T4* encodes **gp57A** (historically also called gp57 or p57), a **small, nonstructural assembly helper/molecular chaperone** that is **required for correct assembly/folding of tail fiber components**—most consistently **gp12 (short tail fiber)** and **gp34 and gp37 (long tail fiber components)**—but is **not incorporated into the mature virion**. |
| GO:0098004 virus tail fiber assembly | IDA PMID:8892827 Characterization of the helper proteins for the assembly of ... | ACCEPT | Summary: Direct experimental characterization demonstrates that gp57A (p57) is required for the assembly of gp12 (short tail fiber) as well as gp34 and gp37 (long tail fiber subunits). Reason: Matsui et al. (PMID:8892827) purified and characterized T4 p57 (gp57A) and established that without functional p57 and its cooperative helper p38, the tail fiber subunits p34, p37, and p12 remain unassembled in infected cells. Supporting Evidence: PMID:8892827 In the absence of the other, p57, p34 (another component of the long tail fiber), p37, and p12 (the subunit of the short tail fiber) remain unassembled. file:BPT4/57/57-deep-research-falcon.md Gene **57** of *Enterobacteria phage T4* encodes **gp57A** (historically also called gp57 or p57), a **small, nonstructural assembly helper/molecular chaperone** that is **required for correct assembly/folding of tail fiber components**—most consistently **gp12 (short tail fiber)** and **gp34 and gp37 (long tail fiber components)**—but is **not incorporated into the mature virion**. |
| GO:0044183 protein folding chaperone | IEA file:BPT4/57/57-uniprot.txt | NEW | Summary: gp57A functions as a molecular chaperone that promotes the folding and trimeric oligomerization of gp12, gp34, and gp37 without becoming part of the assembled fibers. Reason: Existing GOA annotations for gp57A lack a molecular function term. Because gp57A acts transiently to prevent aggregation and catalyze the productive folding and homotrimerization of three distinct fibrous phage proteins (gp12, gp34, and gp37), GO:0044183 (protein folding chaperone) is proposed as its core molecular function. Supporting Evidence: file:BPT4/57/57-uniprot.txt Chaperone essential for folding and oligomerization of both file:BPT4/57/57-deep-research-falcon.md Gene **57** of *Enterobacteria phage T4* encodes **gp57A** (historically also called gp57 or p57), a **small, nonstructural assembly helper/molecular chaperone** that is **required for correct assembly/folding of tail fiber components**—most consistently **gp12 (short tail fiber)** and **gp34 and gp37 (long tail fiber components)**—but is **not incorporated into the mature virion**. |
| GO:0030430 host cell cytoplasm | IEA file:BPT4/57/57-deep-research-falcon.md | NEW | Summary: gp57A is a nonstructural chaperone that operates in the infected Escherichia coli cytoplasm and is excluded from mature virions. Reason: gp57A performs its chaperone function intracellularly within the host bacterial cytoplasm (associated with the inner membrane fraction) during phage morphogenesis and is not incorporated into the mature virion, supporting GO:0030430 (host cell cytoplasm). Supporting Evidence: file:BPT4/57/57-deep-research-falcon.md Gene **57** of *Enterobacteria phage T4* encodes **gp57A** (historically also called gp57 or p57), a **small, nonstructural assembly helper/molecular chaperone** that is **required for correct assembly/folding of tail fiber components**—most consistently **gp12 (short tail fiber)** and **gp34 and gp37 (long tail fiber components)**—but is **not incorporated into the mature virion**. |
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Download this section (compressed HTML)Q: What common sequence or structural motif in the disparate fibrous substrates gp12, gp34, and gp37 is recognized by gp57A, and how does gp57A prevent premature mismatched beta-strand register without requiring ATP hydrolysis?
Q: Does inner-membrane tethering of gp57A in T4-infected Escherichia coli spatially compartmentalize tail fiber folding sites or enhance the local concentration of nascent gp12, gp34, and gp37 monomers?
Experiment: Perform crosslinking mass spectrometry (XL-MS) and NMR titration experiments using 15N-labeled gp57A and unfolded/partially folded fragments of gp12, gp34, and gp37 to map the substrate-binding surface on gp57A and the recognized motifs on its client proteins.
Experiment: Compare in vivo tail fiber assembly efficiency and phage burst size between wild-type gp57A and N-terminally mutated gp57A variants defective in inner-membrane association.
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