BST2 (Chlamydomonas reinhardtii) review notes

UniProt A0A2K3CTQ2 (TrEMBL, "Uncharacterized protein", 450 aa); locus Cre16.g663400 /
CHLRE_16g663400v5. Paralogs: BST1 = Cre16.g662600 -> A0A2K3CTN0 (reviewed in
genes/CHLRE/BST1); BST3 (LCI11) = Cre16.g663450 -> A0A2K3CTP3.

Deep research

Not run. Deep research is unavailable in this session: falcon returns HTTP 402 Payment
Required and the perplexity provider is missing (same result as the BST1 run 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 review.

Identity and family

• Three paralogs clustered on chr 16 PMID:31391312.

• 80% identical; name LCI11 historically used for BST2 and BST3 PMID:31391312. Note that the 2017 interactome uses LCI11 for Cre16.g663450 (BST3).

• Closest land-plant homolog Arabidopsis VCCN1, ~30% identity PMID:31391312.
• Predicted chloroplast transit peptide PMID:31391312.
• Homology model (done for BST1, applies to the >80%-identical group) PMID:31391312.

BST2-specific data

• Expression: induced in ambient CO2; CIA5 dependence partial PMID:31391312, whereas BST1 and BST3
  were severely reduced in cia5. Expressed above BST1 PMID:31391312.
• Localization: Venus fusion (PSAD promoter) in thylakoid membranes, into pyrenoid tubules,
  enriched at pyrenoid periphery PMID:31391312. Native-promoter
  control was done only for BST3.
• Interactome: BST2 is a prey of BST1 and BST3 baits PMID:28938113. LCIB/LCIC interactions were reported for BST3 and BST1 only
  PMID:28938113.
• Phenotype: only via triple RNAi PMID:31391312; no BST2 single mutant.

Family-level physiology (shared with BST1)

• Triple knockdown: poor low-CO2 growth, lower Ci affinity, reduced 14Ci accumulation
  PMID:31391312.
• pmf effect opposite to Arabidopsis vccn1 PMID:31391312.
• HCO3- delivery to CAH3 is a proposal PMID:31391312; no transport data for any of
  BST1-3 PMID:39240724.

Annotation decisions (mirroring BST1)

• GO:0005247 IBA -> MODIFY to GO:0005253 monoatomic anion channel activity.
• GO:0005886 IEA (ARBA "Cell membrane") -> REMOVE; contradicted by 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.
• Module family bst_thylakoid_channel (GO:0005253 on GO:0009535) is supported for BST2 at the
  same (family-inference) strength as for BST1.