chlorosome

GO:0046858 · Membrane organelle · Other · Proposed

A large light-harvesting antenna organelle of green photosynthetic bacteria in which bacteriochlorophyll aggregates self-assemble inside a lipid envelope and attach to the cytoplasmic membrane through a bacteriochlorophyll a-containing CsmA baseplate. [GO:0046858]

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
bacteriochlorophyll c/d/e aggregates	Small molecule	part of			ESSENTIAL	Principal antenna pigments in the chlorosome interior; they self-assemble into lamellar aggregates without a protein scaffold. `DOI:10.1007/s11120-013-9869-3` Orf and Blankenship 2013 review chlorosome pigment self-assembly and identify bacteriochlorophyll c, d, and e as the natural major chlorosome pigments. `DOI:10.1128/JB.00690-09` Psencik et al. 2009 combined cryo-electron microscopy, X-ray scattering, and pigment analysis to show lamellar bacteriochlorophyll aggregates in Chloroflexus aurantiacus chlorosomes.
chlorosome baseplate antenna complex	Protein complex	part of	`cellstructuremech:chlorosome_baseplate_antenna_complex`		ESSENTIAL	Bacteriochlorophyll a-CsmA antenna array that couples the pigment aggregate to downstream membrane reaction-center complexes. `DOI:10.1038/ncomms12454` Nielsen et al. 2016 resolved the CsmA-containing baseplate antenna of Chlorobaculum tepidum chlorosomes in situ. `DOI:10.1128/JB.00690-09` Psencik et al. 2009 visualized the crystalline baseplate lattice on one face of Chloroflexus aurantiacus chlorosomes and linked its lattice dimensions to a CsmA dimer building block.
chlorosome lipid monolayer	Lipid	part of			ESSENTIAL	Surrounds the pigment aggregate as a lipid-rich monolayer that carries chlorosome surface proteins. `DOI:10.1007/s11120-013-9869-3` Orf and Blankenship 2013 describe chlorosomes as bacteriochlorophyll aggregates enclosed by a lipid monolayer with proteins confined to the surface.
accessory chlorosome envelope proteins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	csmB, csmC, csmD, csmE, csmF, csmH, csmI, csmJ, csmK, csmX	UNKNOWN	Additional surface proteins on the chlorosome envelope whose individual roles differ by family and lineage. `DOI:10.1007/s11120-013-9869-3` Orf and Blankenship 2013 review the CsmB, CsmC, CsmD, CsmE, CsmF, CsmH, CsmI, CsmJ, CsmK, and CsmX surface proteins of Chlorobi chlorosomes.

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.

accessory chlorosome envelope proteins

Accession	Protein	Gene	Organism	Entry
`UniProtKB:Q46383`	Chlorosome envelope protein B	csmB	Chlorobaculum tepidum TLS (`NCBITaxon:194439`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene csmB 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/Q46383` UniProtKB reviewed (Swiss-Prot) entry Q46383, the single reviewed entry for gene csmB 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.
`UniProtKB:Q46367`	Chlorosome protein C	csmC	Chlorobaculum tepidum TLS (`NCBITaxon:194439`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene csmC 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/Q46367` UniProtKB reviewed (Swiss-Prot) entry Q46367, the single reviewed entry for gene csmC 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.
`UniProtKB:Q46386`	Chlorosome protein E	csmE	Chlorobaculum tepidum TLS (`NCBITaxon:194439`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene csmE 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/Q46386` UniProtKB reviewed (Swiss-Prot) entry Q46386, the single reviewed entry for gene csmE 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.
`UniProtKB:O68986`	Chlorosome envelope protein F	csmF	Chlorobaculum tepidum TLS (`NCBITaxon:194439`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene csmF 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/O68986` UniProtKB reviewed (Swiss-Prot) entry O68986, the single reviewed entry for gene csmF 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.
`UniProtKB:O68988`	Chlorosome protein I	csmI	Chlorobaculum tepidum TLS (`NCBITaxon:194439`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene csmI 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/O68988` UniProtKB reviewed (Swiss-Prot) entry O68988, the single reviewed entry for gene csmI 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.
`UniProtKB:O68983`	Chlorosome protein J	csmJ	Chlorobaculum tepidum TLS (`NCBITaxon:194439`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene csmJ 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/O68983` UniProtKB reviewed (Swiss-Prot) entry O68983, the single reviewed entry for gene csmJ 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: Chlorosomes are restricted to particular anoxygenic phototrophs, including green sulfur bacteria, filamentous anoxygenic Chloroflexota, and a phototrophic Acidobacteriota lineage. [DOI:10.1007/s11120-013-9869-3]

Canonical examples

NCBITaxon:1097 Chlorobaculum tepidum — Green sulfur bacterium used for in situ NMR, EM, and AFM modelling of the CsmA baseplate. [DOI:10.1038/ncomms12454]
NCBITaxon:1108 Chloroflexus aurantiacus — Green filamentous Chloroflexota model whose thin chlorosomes revealed baseplate and lamellar pigment architecture by cryo-EM and X-ray scattering. [DOI:10.1128/JB.00690-09]

Functions

photosynthetic light harvesting — Chlorosomes harvest weak light with dense bacteriochlorophyll aggregates and transfer excitation energy through the baseplate to membrane photosynthetic reaction centers.
- DOI:10.1007/s11120-010-9533-0 Oostergetel et al. 2010 review the chlorosome as a highly efficient photosynthetic light-harvesting antenna.
- DOI:10.1007/s11120-013-9869-3 Orf and Blankenship 2013 describe chlorosomes as the distinguishing antenna complexes of green photosynthetic bacteria.

Mechanism graphs

Self-assembled pigments feed excitation energy into the baseplate (FUNCTION)

Bacteriochlorophyll c/d/e pigments self-assemble inside a lipid monolayer, while CsmA builds a bacteriochlorophyll a-containing baseplate on one side of the chlorosome. The baseplate couples the dense pigment aggregate to downstream membrane reaction-center proteins so dim light can be harvested for anoxygenic photosynthesis.

Subject	Predicate	Object	Evidence
bacteriochlorophyll c/d/e aggregates	self-assembles inside	chlorosome	`DOI:10.1007/s11120-013-9869-3` Orf and Blankenship 2013 review pigment-pigment assembly of the main chlorosome antenna bacteriochlorophylls. `DOI:10.1128/JB.00690-09` Psencik et al. 2009 resolved lamellar bacteriochlorophyll aggregates in Chloroflexus aurantiacus chlorosomes.
chlorosome lipid monolayer	surrounds	bacteriochlorophyll c/d/e aggregates	`DOI:10.1007/s11120-013-9869-3` Orf and Blankenship 2013 describe a lipid monolayer around the chlorosome pigment aggregate.
CsmA baseplate antenna	forms	chlorosome	`DOI:10.1038/ncomms12454` Nielsen et al. 2016 resolved the in situ baseplate antenna structure and modelled the CsmA array of Chlorobaculum tepidum.
bacteriochlorophyll c/d/e aggregates	transfers excitation to	CsmA baseplate antenna	`DOI:10.1007/s11120-010-9533-0` Oostergetel et al. 2010 review the chlorosome-to-baseplate energy-transfer step.
CsmA baseplate antenna	couples to	membrane reaction-center acceptor chain	`DOI:10.1038/ncomms12454` Nielsen et al. 2016 describe the baseplate as the high-efficiency antenna between chlorosome pigments and downstream reaction-center proteins.
membrane reaction-center acceptor chain	supports	photosynthesis	`DOI:10.1007/s11120-013-9869-3` Orf and Blankenship 2013 place chlorosomes in the photosynthetic apparatus of green bacteria as antennae feeding reaction centers.

Discussions

CURATION_TODO (OPEN): Find exact InterPro or Pfam families for the accessory Csm envelope proteins, or document why each remains reviewed-label-only. The chlorosome baseplate component is now grounded to an internal CellStructureMech record that tracks exact CsmA-family grounding as its own boundary question; this TODO remains for the accessory chlorosome-surface proteins.

Evidence

DOI:10.1007/s11120-013-9869-3 Orf GS and Blankenship RE 2013, Chlorosome antenna complexes from green photosynthetic bacteria, Photosynthesis Research.
DOI:10.1007/s11120-010-9533-0 Oostergetel GT, van Amerongen H and Boekema EJ 2010, The chlorosome: a prototype for efficient light harvesting in photosynthesis, Photosynthesis Research.
DOI:10.1128/JB.00690-09 Psencik J et al. 2009, Structure of chlorosomes from the green filamentous bacterium Chloroflexus aurantiacus, Journal of Bacteriology.
DOI:10.1038/ncomms12454 Nielsen JT et al. 2016, In situ high-resolution structure of the baseplate antenna complex in Chlorobaculum tepidum, Nature Communications.

Curation history

2026-09-04T07:48:46Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-04T07:50:00Z claude · EXPANDED_RECORD — Added chlorosome composition, taxonomy, functions, literature evidence, a function graph, and a protein-family grounding todo.
2026-09-08T07:39:28Z uniprot_genes · SEED_PROTEIN_EXAMPLES — #183: added 7 protein example(s) by resolving each of the component's declared gene symbols to the single reviewed UniProtKB entry for that symbol in a taxon this record names, deduplicated by accession. Symbols resolving to more than one reviewed entry were skipped rather than chosen between.
2026-09-13T07:47:31Z codex · REFINED_RECORD — Grounded the chlorosome CsmA baseplate component to the newly minted chlorosome baseplate antenna complex record and narrowed the component grounding TODO to accessory Csm proteins.

Source: data/structures/membrane_organelle/chlorosome.yaml