chlorosome baseplate antenna complex

cellstructuremech:chlorosome_baseplate_antenna_complex · Energy complex · Multiprotein complex · Proposed

A bacteriochlorophyll a-CsmA light-harvesting protein-pigment array on one face of green bacterial chlorosomes that accepts excitation energy from chlorosome bacteriochlorophyll aggregates and couples it toward membrane reaction-center complexes. [DOI:10.1038/ncomms12454]

Synonyms: CsmA baseplate antenna; CsmA bacteriochlorophyll a baseplate; protein-pigment baseplate complex

Part of: chlorosome (GO:0046858); chlorosome envelope (GO:0033105)

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
CsmA baseplate apoprotein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	csmA		ESSENTIAL	Small bacteriochlorophyll a-binding apoprotein that oligomerizes into the two-dimensional paracrystalline baseplate lattice. `DOI:10.1038/ncomms12454` Nielsen et al. 2016 resolved CsmA as the protein building block of the in situ baseplate antenna in Chlorobaculum tepidum chlorosomes. `PMID:20077007` Pedersen et al. 2010 modeled the protein-pigment baseplate complex of green-bacterial chlorosomes.
bacteriochlorophyll a	Small molecule	part of	`CHEBI:30033`			ESSENTIAL	Baseplate pigment bound by CsmA subunits and tuned for excitation transfer out of the chlorosome. `DOI:10.1038/ncomms12454` Nielsen et al. 2016 modeled bacteriochlorophyll a pigments inside the CsmA baseplate antenna complex.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

CsmA baseplate apoprotein

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P0A314`	Bacteriochlorophyll c-binding protein	csmA	Chlorobaculum tepidum TLS (`NCBITaxon:194439`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene csmA in Chlorobaculum tepidum TLS, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `https://www.uniprot.org/uniprotkb/P0A314` UniProtKB reviewed (Swiss-Prot) entry P0A314, the single reviewed entry for gene csmA in Chlorobaculum tepidum TLS. Establishes the accession and gene identity only; the component's membership in this structure rests on the record's own sources.

Taxonomic distribution

NCBITaxon:2 Bacteria — VARIABLE: CsmA chlorosome baseplates occur in the chlorosomes of particular anoxygenic green-bacterial phototrophs rather than broadly across bacteria. [DOI:10.1007/s11120-013-9869-3]

Canonical examples

NCBITaxon:1097 Chlorobaculum tepidum — Green sulfur bacterium whose intact chlorosomes were used to resolve the CsmA baseplate antenna structure in situ. [DOI:10.1038/ncomms12454]
NCBITaxon:1108 Chloroflexus aurantiacus — Green filamentous bacterium whose chlorosomes exposed a crystalline baseplate lattice linked to the CsmA dimer building block. [DOI:10.1128/JB.00690-09]

Functions

photosynthesis, light harvesting GO:0009765 — The chlorosome baseplate accepts excitation energy from self-assembled chlorosome bacteriochlorophyll aggregates and passes it toward downstream membrane reaction-center complexes.
- DOI:10.1038/ncomms12454 Nielsen et al. 2016 resolved the CsmA baseplate antenna and modeled the pigment arrangement that transfers excitation energy out of Chlorobaculum tepidum chlorosomes.
- DOI:10.1007/s11120-010-9533-0 Oostergetel et al. 2010 review chlorosome-to-baseplate excitation transfer as part of green-bacterial light harvesting.

Mechanism graphs

The CsmA baseplate routes chlorosome excitation outward (FUNCTION)

CsmA apoproteins bind bacteriochlorophyll a to form the two-dimensional chlorosome baseplate antenna. The baseplate accepts excitation from bacteriochlorophyll aggregates and routes it toward membrane reaction-center complexes.

Subject	Predicate	Object	Evidence
CsmA baseplate apoprotein	oligomerizes into	chlorosome baseplate antenna complex	`DOI:10.1038/ncomms12454` Nielsen et al. 2016 resolved an in situ baseplate structure built from rows of CsmA subunits in Chlorobaculum tepidum chlorosomes.
bacteriochlorophyll a	binds to	CsmA baseplate apoprotein	`DOI:10.1038/ncomms12454` Nielsen et al. 2016 modeled the bacteriochlorophyll a-CsmA organization of the baseplate antenna.
chlorosome bacteriochlorophyll aggregate	transfers excitation to	chlorosome baseplate antenna complex	`DOI:10.1007/s11120-010-9533-0` Oostergetel et al. 2010 review the chlorosome-to-baseplate excitation-transfer step.
chlorosome baseplate antenna complex	couples to	membrane reaction-center acceptor chain	`DOI:10.1038/ncomms12454` Nielsen et al. 2016 describe the baseplate as the antenna between chlorosome pigments and downstream reaction-center proteins.
chlorosome baseplate antenna complex	contributes to	photosynthesis, light harvesting	`DOI:10.1007/s11120-013-9869-3` Orf and Blankenship 2013 review chlorosomes, including their CsmA baseplates, as the light-harvesting antennae of green photosynthetic bacteria.

Discussions

CURATION_TODO (OPEN): Resolve an exact source-neutral InterPro, Pfam, or NCBIfam identifier for chlorosome CsmA before grounding the CsmA apoprotein component. This record grounds the whole baseplate to CellStructureMech and the pigment to ChEBI, but it does not guess whether available protein-family terms exactly denote the green-bacterial CsmA baseplate apoprotein family.

Evidence

DOI:10.1038/ncomms12454 Nielsen et al. 2016, In situ high-resolution structure of the baseplate antenna complex in Chlorobaculum tepidum, Nature Communications.
PMID:20077007 Pedersen et al. 2010, A model of the protein-pigment baseplate complex in chlorosomes of photosynthetic green bacteria, Photosynthesis Research.
DOI:10.1128/JB.00690-09 Psencik et al. 2009, Structure of chlorosomes from the green filamentous bacterium Chloroflexus aurantiacus, Journal of Bacteriology.
DOI:10.1007/s11120-013-9869-3 Orf and Blankenship 2013, Chlorosome antenna complexes from green photosynthetic bacteria, Photosynthesis Research.
GO:0030076 Gene Ontology cellular-component term for the broader light-harvesting complex class.
GO:0046858 Gene Ontology cellular-component term for chlorosome; the definition states that chlorosomes attach to the cytoplasmic membrane via a bacteriochlorophyll a-containing protein baseplate.
GO:0033105 Gene Ontology cellular-component term for the chlorosome envelope.
GO:0009765 Gene Ontology biological-process term for photosynthesis, light harvesting.
CHEBI:30033 ChEBI term for bacteriochlorophyll a.

Curation history

2026-09-13T07:46:31Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-13T07:47:31Z codex · EXPANDED_RECORD — Added chlorosome and envelope parthood, CsmA and bacteriochlorophyll a components, green-bacterial scope, Chlorobaculum and Chloroflexus examples, a light-harvesting function, GO/ChEBI/DOI/PMID evidence, a nonmechanistic excitation-transfer graph, and a CsmA-family grounding TODO.
2026-09-13T07:58:10Z codex · ADDRESS_REVIEW — #764: corrected the Pedersen et al. 2010 evidence note so it describes the baseplate model paper rather than calling it a review.

Source: data/structures/energy_complex/chlorosome_baseplate_antenna_complex.yaml