id: Q88CX7
gene_symbol: secB
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:160488
  label: Pseudomonas putida (strain ATCC 47054 / DSM 6125 / CFBP 8728 / NCIMB 11950 / KT2440)
description: SecB is a soluble cytoplasmic export chaperone that binds a subset of newly synthesized Sec
  precursors, prevents their premature folding, and delivers them to the SecA motor in a translocation-competent
  state. It functions as a homotetramer in the post-translational branch of bacterial Sec export.
existing_annotations:
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: located_in
  review:
    summary: SecB is a soluble cytoplasmic preprotein chaperone.
    action: ACCEPT
    reason: Cytoplasmic localization is integral to SecB capture of newly synthesized export precursors.
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IEA
  original_reference_id: GO_REF:0000104
  qualifier: involved_in
  review:
    summary: SecB prevents premature folding rather than catalyzing protein folding.
    action: REMOVE
    reason: >-
      The conserved SecB mechanism maintains export substrates in an unfolded,
      translocation-competent state. GO:0140309 captures both binding and escort
      of that substrate, so a separate generic unfolded-protein-binding term would
      be redundant rather than filling a functional gap.
- term:
    id: GO:0015031
    label: protein transport
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: involved_in
  review:
    summary: SecB delivers unfolded precursors into the bacterial Sec export pathway.
    action: MODIFY
    reason: Protein transport is correct but too broad; the direct process is transport by the Sec complex.
    proposed_replacement_terms:
    - id: GO:0043952
      label: protein transport by the Sec complex
- term:
    id: GO:0051262
    label: protein tetramerization
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: The functional SecB chaperone is a homotetramer.
    action: KEEP_AS_NON_CORE
    reason: Tetramerization describes conserved assembly but not the substrate-carrier output.
- term:
    id: GO:0140309
    label: unfolded protein holdase activity
  evidence_type: ISS
  original_reference_id: file:PSEPK/secB/secB-uniprot.txt
  qualifier: enables
  review:
    summary: SecB carries unfolded precursor proteins from the cytoplasm to its SecA receptor.
    action: NEW
    reason: This live carrier term captures the conserved SecB mechanism more precisely than protein folding.
    supported_by:
    - reference_id: file:PSEPK/secB/secB-uniprot.txt
      supporting_text: binds to a subset of precursor proteins, maintaining them in a translocation-competent state.
    - reference_id: PMID:16962134
      supporting_text: >-
        Capture of the precursor polypeptides before they fold is achieved by the
        promiscuous binding to the chaperone SecB. SecB delivers its ligand to export
        sites through its specific binding to SecA, a peripheral component of the
        membrane translocon. At the translocon the ligand is passed from SecB to SecA
        and subsequently through the SecYEG channel.
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO terms
  findings: []
- id: GO_REF:0000104
  title: Electronic Gene Ontology annotations created by transferring manual GO annotations between related
    proteins based on shared sequence features
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:16962134
  title: Sites of interaction of a precursor polypeptide on the export chaperone SecB mapped by site-directed spin labeling.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: PubMed abstract directly verifies unfolded-preprotein capture, SecA delivery, and SecYEG handoff.
- id: file:PSEPK/secB/secB-uniprot.txt
  title: UniProtKB entry for secB (Q88CX7)
  findings:
  - statement: The local record provides the exact family, topology, and conserved functional description
      used in this review.
- id: file:PSEPK/secB/secB-goa.tsv
  title: QuickGO GOA annotations for secB
  findings:
  - statement: The fetched table is the complete existing-annotation set reviewed here.
- id: file:projects/P_PUTIDA/deep-research/PSEPK__sec-protein-export__ppu03060-deep-research-openscientist.md
  title: OpenScientist PSEPK protein-export pathway synthesis
  findings:
  - statement: The report confirms pathway completeness and separates Sec, SRP, Tat, YidC, signal-peptidase,
      and Xcp boundaries.
- id: file:modules/bacterial_sec_posttranslational_protein_export.yaml
  title: Bacterial post-translational Sec protein-export module
  findings:
  - statement: The reusable module assigns each molecular function to the appropriate leaf protein or
      complex subunit.
aliases:
- PP_5053
core_functions:
- description: Binds and escorts unfolded Sec precursor proteins to SecA while maintaining them in a translocation-competent
    state.
  supported_by:
  - reference_id: file:PSEPK/secB/secB-uniprot.txt
    supporting_text: binds to a subset of precursor proteins, maintaining them in a translocation-competent state.
  - reference_id: PMID:16962134
    supporting_text: >-
      SecB delivers its ligand to export sites through its specific binding to SecA,
      a peripheral component of the membrane translocon.
  molecular_function:
    id: GO:0140309
    label: unfolded protein holdase activity
  directly_involved_in:
  - id: GO:0043952
    label: protein transport by the Sec complex
  locations:
  - id: GO:0005737
    label: cytoplasm
suggested_questions:
- question: Which KT2440 exported proteins depend specifically on SecB rather than cotranslational targeting?
suggested_experiments:
- description: Compare precursor accumulation and export efficiency in wild type and a secB-depleted strain,
    then test direct binding of purified SecB to representative precursor proteins and SecA.
  experiment_type: Sec-pathway mechanism validation