stalk crossband

cellstructuremech:stalk_crossband · Appendage · Multiprotein complex · Proposed

A disk-like multiprotein diffusion barrier that spans the Caulobacter stalk cross-section. StpABCD-containing stalk crossbands partition the prostheca into compartments by limiting exchange of soluble and membrane proteins between the cell body and stalk segments. [DOI:10.1016/j.cell.2012.10.046]

Synonyms: stalk band; Caulobacter crossband

Part of: prostheca (cellstructuremech:prostheca)

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
StpA/StpB crossband scaffold proteins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	stpA, stpB		ESSENTIAL	Form the basic crossband scaffold in Caulobacter. StpAB-deficient cells lack microscopically discernible crossbands, while StpC/D-deficient cells retain them. `DOI:10.1016/j.cell.2012.10.046` Schlimpert et al. 2012 show loss of visible crossbands after stpAB deletion and a hierarchical StpA/StpB assembly scaffold, distinct from StpC/D-dependent sealing.
StpC/StpD crossband barrier-sealing proteins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	stpC, stpD		DISPENSABLE	Seal the StpA/StpB scaffold to produce an efficient protein diffusion barrier. Structural essentiality is DISPENSABLE because crossbands remain visible without StpC/D, but those barriers are leaky; this does not mean normal barrier function is dispensable. `DOI:10.1016/j.cell.2012.10.046` Schlimpert et al. 2012 observe visible crossbands in stpC/stpD mutants and partial loss of periplasmic compartmentalization in the stpCD deletion strain, distinguishing structural formation from barrier sealing.

Taxonomic distribution

NCBITaxon:2 Bacteria — VARIABLE: Stalk crossbands have been described in stalks of Caulobacter and Asticcacaulis, but are absent from most bacterial morphologies. [DOI:10.1128/JB.178.13.3939-3948.1996]
NCBITaxon:155892 Caulobacter vibrioides — UNIVERSAL: Crossbands form along the Caulobacter stalk as part of the stalked-cell program. [DOI:10.1016/j.cell.2012.10.046]

Canonical examples

NCBITaxon:565050 Caulobacter vibrioides NA1000 — Model strain used to identify the proteinaceous StpABCD diffusion barriers in the stalk. [DOI:10.1016/j.cell.2012.10.046]

Functions

stalk diffusion barrier — Crossbands restrict soluble and membrane-protein exchange between the cell body and the prostheca, and between neighboring stalk compartments.
- DOI:10.1016/j.cell.2012.10.046 Schlimpert et al. 2012 show that crossbands block diffusion across Caulobacter stalk compartments.

Mechanism graphs

StpABCD proteins assemble stalk-compartment diffusion barriers (ASSEMBLY)

In Caulobacter, StpA and StpB form the crossband scaffold; StpC and StpD tighten its diffusion barrier. Crossbands span the prostheca, and intact barriers limit soluble and membrane-protein exchange across stalk compartments.

Subject	Predicate	Object	Evidence
StpA/StpB crossband scaffold proteins	forms scaffold of	stalk crossband	`DOI:10.1016/j.cell.2012.10.046` Schlimpert et al. 2012 show loss of visible crossbands after stpAB deletion and a hierarchical StpA/StpB assembly scaffold, distinct from StpC/D-dependent sealing.
StpC/StpD crossband barrier-sealing proteins	seals diffusion barrier of	stalk crossband	`DOI:10.1016/j.cell.2012.10.046` Schlimpert et al. 2012 observe visible crossbands in stpC/stpD mutants and partial loss of periplasmic compartmentalization in the stpCD deletion strain, distinguishing structural formation from barrier sealing.
stalk crossband	spans	prostheca	`DOI:10.1016/j.cell.2012.10.046` Schlimpert et al. 2012 describe crossbands as spanning the stalk. `PMID:4126821` Jones and Schmidt 1973 imaged electron-dense crossbands in Caulobacter stalks.
stalk crossband	restricts	protein diffusion	`DOI:10.1016/j.cell.2012.10.046` Schlimpert et al. 2012 tested soluble and membrane-protein diffusion across crossbands.
stalk crossband	supports	stalk compartmentalization	`DOI:10.1016/j.cell.2012.10.046` Schlimpert et al. 2012 connect crossband diffusion barriers with bacterial stalk compartments.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral groundings for the Caulobacter StpABCD crossband complex. The first record uses a reviewed label for the StpABCD cohort until an exact protein-family or complex identifier is verified. Reassessment on 2026-10-11: The record separates the StpAB scaffold cohort from StpCD sealing constituents. Both use reviewed labels until exact protein-family or complex identifiers are verified; historical StpABCD membership is retained without conflating their structural essentiality.
CURATION_TODO (RESOLVED): Model the stalk crossband as a protein complex part of the prostheca, not as a molecular constituent of the prostheca record. The prostheca record captures the whole envelope projection and its generic wall and membrane materials. Crossbands are discrete proteinaceous barriers inside that projection, so they receive a separate record with part_of pointing back to the prostheca.

Evidence

DOI:10.1016/j.cell.2012.10.046 Schlimpert S et al. 2012, 'General protein diffusion barriers create compartments within bacterial cells', Cell.
DOI:10.1128/JB.178.13.3939-3948.1996 Poindexter JS and Staley JT 1996, 'Caulobacter and Asticcacaulis stalk bands as indicators of stalk age', Journal of Bacteriology.
PMID:4126821 Jones HC and Schmidt JM 1973, 'Ultrastructural study of crossbands occurring in the stalks of Caulobacter crescentus', Journal of Bacteriology.

Curation history

2026-09-11T03:29:52Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-11T03:30:17Z codex · EXPANDED_RECORD — Added stalk-band synonymy, protein-complex parentage, prostheca parthood, StpABCD constituent proteins, Caulobacter taxonomy, diffusion-barrier and stalk-age functions, a StpABCD assembly graph, DOI/PMID evidence, and grounding/boundary discussions.
2026-09-11T03:30:33Z codex · REFINED_COMPONENTS — Narrowed the StpABCD row from a protein-complex component to a protein cohort so the component table does not duplicate the stalk crossband record itself.
2026-09-11T03:37:39Z codex · ADDRESS_REVIEW — Resolved PR #401 issues #402 and #403 by removing stalk-age marking from functions and replacing the stalk-compartments state with a stalk-compartmentalization biological-process graph node.
2026-10-11T05:53:03Z codex · ADDRESS_SAVED_REVIEW — Addressed #2179: split StpAB structural scaffold from StpCD barrier-sealing constituents, assigned structural rather than functional essentiality, and updated graph references and the existing grounding discussion.
2026-10-11T06:33:26Z codex · ADDRESS_SAVED_REVIEW — Addressed #2185: Restored the exact original StpABCD grounding rationale and retained the scaffold/sealing explanation as a dated append-only reassessment.

Source: data/structures/appendage/stalk_crossband.yaml