phycobilisome core

cellstructuremech:phycobilisome_core · Energy complex · Multiprotein complex · Proposed

Allophycocyanin-containing central cylinder assembly of a phycobilisome that receives excitation energy from peripheral rods and routes it toward chlorophyll photosystems. [DOI:10.1146/annurev-biophys-062920-063657]

Synonyms: allophycocyanin core

Part of: phycobilisome (GO:0030089)

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

Components

Component	Type	Part of / acts on	Grounding	Genes	Essential	Role
allophycocyanin core phycobiliproteins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	apcA, apcB	ESSENTIAL	Core allophycocyanin alpha and beta subunits that assemble into the central phycobilisome core cylinders and carry tuned bilin chromophores for rod-to-photosystem excitation transfer. `DOI:10.1146/annurev-biophys-062920-063657` Sui 2021 reviews the allophycocyanin core as the central cylinder assembly that accepts excitation from peripheral phycobilisome rods. `DOI:10.1038/s41467-021-25813-y` Sauer et al. 2021 resolved PCC 7002 and PCC 7120 allophycocyanin core subunits within intact phycobilisomes by cryo-EM.
phycobilisome core linker and terminal emitter polypeptides	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	apcC, apcD, apcE, apcF	UNKNOWN	Core linker and terminal-emitter polypeptides that stabilize the allophycocyanin core and tune final excitation transfer toward chlorophyll photosystems. `DOI:10.1146/annurev-biophys-062920-063657` Sui 2021 reviews core linker and terminal-emitter roles in phycobilisome assembly and downhill energy transfer. `DOI:10.1038/s41467-021-25813-y` Sauer et al. 2021 modeled PCC 7002 and PCC 7120 core linkers and terminal emitters in light-harvesting and photoprotected phycobilisome states.
allophycocyanin-bound phycobilin chromophores	Small molecule	part of	Reviewed label only (reviewed name; no accession asserted)		ESSENTIAL	Covalently attached linear tetrapyrrole pigments that absorb and relay excitation within the allophycocyanin core. `DOI:10.1146/annurev-biophys-062920-063657` Sui 2021 reviews allophycocyanin-bound phycobilins as the energy-transfer chromophores of the phycobilisome core.

Taxonomic distribution

NCBITaxon:1117 Cyanobacteriota — COMMON: Cyanobacterial phycobilisomes contain allophycocyanin cores that accept excitation from peripheral rods. [DOI:10.1146/annurev-biophys-062920-063657]
NCBITaxon:2763 Rhodophyta — COMMON: Red algal phycobilisomes share the core-and-rod architecture in which a central allophycocyanin core collects excitation from rods. [DOI:10.1146/annurev-biophys-062920-063657]

Canonical examples

NCBITaxon:32049 Picosynechococcus sp. PCC 7002 — Cyanobacterial model whose phycobilisome core was resolved by cryo-EM to model core-mediated excitation transfer. [DOI:10.1038/s41467-021-25813-y]
NCBITaxon:32053 Thermostichus vulcanus — Thermophilic cyanobacterium whose core and rods were resolved in an intact light-harvesting phycobilisome. [DOI:10.1038/s41467-022-30962-9]

Functions

photosynthesis, light harvesting GO:0009765 — The phycobilisome core receives excitation from peripheral phycobiliprotein rods and transfers it through terminal emitters toward chlorophyll-containing photosystems.
- DOI:10.1146/annurev-biophys-062920-063657 Sui 2021 reviews rod-to-core energy transfer through allophycocyanin and terminal emitters in phycobilisomes.
- DOI:10.1038/s41467-021-25813-y Sauer et al. 2021 modeled excitation-energy transfer through cyanobacterial phycobilisome cores.

Mechanism graphs

The allophycocyanin core routes rod excitation to photosystems (FUNCTION)

Peripheral phycobilisome rods transfer captured excitation to the central allophycocyanin core. Core bilins and terminal emitters route that energy toward chlorophyll-containing photosystems.

Subject	Predicate	Object	Evidence
allophycocyanin core phycobiliproteins	assemble into	phycobilisome core	`DOI:10.1038/s41467-021-25813-y` Sauer et al. 2021 resolved allophycocyanin subunits in the PCC 7002 and PCC 7120 cores by cryo-EM.
phycobilisome core linker and terminal emitter polypeptides	stabilize and tune	phycobilisome core	`DOI:10.1146/annurev-biophys-062920-063657` Sui 2021 reviews core linker and terminal emitter positions in the allophycocyanin core.
allophycocyanin-bound phycobilin chromophores	are bound by	allophycocyanin core phycobiliproteins	`DOI:10.1146/annurev-biophys-062920-063657` Sui 2021 reviews the bilins carried by allophycocyanin core subunits.
phycobilisome peripheral rods	transfer excitation to	phycobilisome core	`DOI:10.1146/annurev-biophys-062920-063657` Sui 2021 describes the rod-to-core direction of energy transfer in phycobilisomes.
phycobilisome core	transfers excitation to	chlorophyll photosystems	`DOI:10.1038/s41467-021-25813-y` Sauer et al. 2021 modeled energy transfer through the PCC 7002 allophycocyanin core toward photosystem acceptors.
phycobilisome core	contributes to	photosynthesis, light harvesting	`DOI:10.1146/annurev-biophys-062920-063657` Sui 2021 reviews core-mediated excitation transfer as part of phycobilisome light harvesting.

Discussions

CURATION_TODO (OPEN): Resolve exact InterPro, Pfam, NCBIfam, Complex Portal or ChEBI accessions for phycobilisome core allophycocyanins, terminal emitters, core linkers and bound phycobilins. This first child record keeps mixed allophycocyanin, terminal emitter, core-linker and chromophore sets reviewed-label-only because a broad phycobiliprotein family or phycobilin class could blur core constituents with peripheral rod constituents.
INTERPRETATION (RESOLVED): Keep the phycobilisome core distinct from the whole phycobilisome and from peripheral phycobilisome rods. GO:0030089 denotes the complete phycobilisome. The core is a named allophycocyanin-containing subassembly of the complete antenna, while peripheral rods contain different phycobiliproteins and dock onto the core.

Evidence

DOI:10.1146/annurev-biophys-062920-063657 Sui 2021, Structure of Phycobilisomes, Annual Review of Biophysics.
DOI:10.1038/s41467-021-25813-y Sauer et al. 2021, Structural insight into the mechanism of energy transfer in cyanobacterial phycobilisomes, Nature Communications.
DOI:10.1038/s41467-022-30962-9 Kawakami et al. 2022, Core and rod structures of a thermophilic cyanobacterial light-harvesting phycobilisome, Nature Communications.
GO:0030076 Gene Ontology cellular-component term for the broader light-harvesting complex class.
GO:0030089 Gene Ontology cellular-component term for the containing phycobilisome complex.
GO:0009765 Gene Ontology biological-process term for photosynthesis, light harvesting.
InterPro:IPR012128 InterPro family for phycobilisome alpha/beta subunits; broader than the allophycocyanin-only core phycobiliproteins because it also includes peripheral rod phycobiliproteins.
InterPro:IPR006245 InterPro family for allophycocyanin beta subunits; narrower than the complete alpha/beta core phycobiliprotein component.
InterPro:IPR011134 InterPro family for allophycocyanin linker proteins; narrower than the combined phycobilisome core linker and terminal emitter set.

Curation history

2026-10-03T01:45:06Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-03T01:46:19Z codex · EXPANDED_RECORD — Added light-harvesting-complex parentage, phycobilisome parthood, allophycocyanin/core-linker/phycobilin components, cyanobacterial and red-algal scope, Synechocystis and Thermostichus examples, a light-harvesting function, DOI/GO evidence, a nonmechanistic core energy-transfer graph, and grounding and boundary discussions.
2026-10-03T01:48:13Z codex · REFINE_GROUNDING_DECISIONS — Recorded rejected InterPro near matches IPR012128, IPR006245 and IPR011134 in the phycobilisome-core component grounding notes.
2026-10-03T02:02:33Z codex · REVIEW_FIX_SAUER_TAXON — #1961: replaced unsupported Synechocystis PCC 6803 attribution for Sauer 2021 with Picosynechococcus sp. PCC 7002 and strain-neutral PCC 7002/PCC 7120 evidence notes.

Source: data/structures/energy_complex/phycobilisome_core.yaml