BST3 (Chlamydomonas reinhardtii) review notes

UniProt A0A2K3CTP3 (TrEMBL, "Uncharacterized protein", 466 aa); locus Cre16.g663450 /
CHLRE_16g663450v5. Called LCI11 in the 2017 interactome. Paralogs: BST1 = Cre16.g662600 ->
A0A2K3CTN0 (genes/CHLRE/BST1); BST2 = Cre16.g663400 -> A0A2K3CTQ2 (genes/CHLRE/BST2).

Deep research

Not run. Deep research is unavailable in this session: falcon returns HTTP 402 Payment
Required and the perplexity provider is missing (same as for the BST1 and BST2 runs on
2026-10-03). No deep-research file exists; this review is built from the primary literature
cached in publications/ and stays consistent with the sibling BST1/BST2 reviews.

Identity and family

• Three paralogs clustered on chr 16 PMID:31391312.
• LCI11 name and >80% identity PMID:31391312. Fang et al. = PMID:22634760 (verified
  via PubMed esearch/esummary); the cached text of that paper does not mention LCI11 or
  Cre16.g663450 (gene data are in uncached supplementary tables). The 2017 interactome uses
  LCI11 specifically for Cre16.g663450 PMID:28938113. A PubMed search for "LCI11 Chlamydomonas" returns no hits.
• Predicted chloroplast transit peptide PMID:31391312.
• Homology model of the group: PMID:31391312.
• UniProt subcellular location "Cell membrane" is an ARBA default for bestrophins
  (ARBA00004651); contradicted by experiment.

BST3-specific data

• Expression: low-CO2 induced within 2 h PMID:31391312; strongly CIA5-dependent PMID:31391312.
• Localization: the only paralog imaged from its native promoter PMID:31391312; thylakoid membranes
  extending into pyrenoid tubules PMID:31391312.
• Interactome (LCI11 bait): LCIB, LCIC, BST1, BST2 [PMID:28938113 "Both LCIB and LCIC interact
  with LCI11 (Cre16.g663450), and LCIC also interacts with Cre16.g662600"; "LCI11 and
  Cre16.g662600 directly interact, and both also interact with another bestrophin-like
  protein, Cre16.g663400."].
• Single mutant: CLiP bst3 (LMJ.RY0402.089365), protein-null PMID:31391312, weak phenotype, implying redundancy PMID:31391312.

Family-level physiology (shared with BST1/BST2)

• Triple knockdown: poor low-CO2 growth, lower Ci affinity PMID:31391312.
• pmf effect opposite to Arabidopsis vccn1 PMID:31391312.
• HCO3- delivery to CAH3 is a proposal PMID:31391312; no transport data
  PMID:39240724.

Annotation decisions (mirroring BST1/BST2)

• GO:0005247 IBA -> MODIFY to GO:0005253 monoatomic anion channel activity.
• GO:0005886 IEA (ARBA "Cell membrane") -> REMOVE; contradicted by native-promoter thylakoid
  localization.
• GO:0019684 IBA -> MARK_AS_OVER_ANNOTATED (VCCN1-specific pmf role; divergent in BST1-3).
• GO:0042651 IBA -> ACCEPT.
• GO:1902476 IEA -> MODIFY to GO:0098656 monoatomic anion transmembrane transport.
• NEW GO:0009535 chloroplast thylakoid membrane, IDA PMID:31391312.
• No NEW BP term: bst3 single mutant phenotype is weak and the triple-RNAi Ci-uptake defect is
  necessity evidence shared by three paralogs; the CCM process role stays in core_functions
  prose.
• Module family bst_thylakoid_channel (GO:0005253 on GO:0009535) is supported for BST3 at
  the same family-inference strength as for BST1/BST2; BST3 has the strongest location
  evidence of the three.