Literature summary for 4.2.1.1 extracted from

Koh, C.Z.Y.; Hiong, K.C.; Choo, C.Y.L.; Boo, M.V.; Wong, W.P.; Chew, S.F.; Neo, M.L.; Ip, Y.K.
Molecular characterization of a dual domain carbonic anhydrase from the ctenidium of the giant clam, Tridacna squamosa, and its expression levels after light exposure, cellular localization, and possible role in the uptake of exogenous inorganic carbon (2018), Front. Physiol., 9, 281 .

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Cloned(Commentary)

Cloned (Comment)	Organism
DNA and amino acid sequence determination and analysis, sequence comparisons and phylogenetic tree	Tridacna squamosa

Localization

Localization	Comment	Organism	GeneOntology No.	Textmining
membrane	membrane-bound, at apical membrane of some epithelial cells surrounding the tertiary water channels and to a lesser extent at the apical membrane of some epithelial apical immunofluorescence epithelial cells as compared with the control. Presence of two transmembrane regions in the DDCA	Tridacna squamosa	16020	-
additional information	the signal peptide (residue 1-22) is predicted to be extracellular, and the GPI anchor is predicted to be Ala576 located near the 3' end of the second CA domain	Tridacna squamosa	-	-

Metals/Ions

Metals/Ions	Comment	Organism	Structure
Zn2+	required, zinc enzyme, one of the Zn2+-containing active sites might be located externally and the other one inside the cell. Conserved histidine residues (His116, His118, His141) coordinate the Zn2+-containing catalytic site	Tridacna squamosa

Natural Substrates/ Products (Substrates)

Natural Substrates	Organism	Comment (Nat. Sub.)	Natural Products	Comment (Nat. Pro.)	Rev.	Reac.
H2CO3	Tridacna squamosa	-	CO2 + H2O	-	r

Organism

Organism	UniProt	Comment	Textmining
Tridacna squamosa	A0A2R2Y2Q1	-	-

Source Tissue

Source Tissue	Comment	Organism	Textmining
ctenidium	DDCA is expressed predominantly in the ctenidium	Tridacna squamosa	-
epithelial cell	at apical membrane of some epithelial cells surrounding the tertiary water channels and to a lesser extent at the apical membrane of some epithelial apical immunofluorescence epithelial cells as compared with the control	Tridacna squamosa	-
mantle	-	Tridacna squamosa	-
additional information	the DDCA is localized apically in certain epithelial cells near the base of the ctenidial filament and the epithelial cells surrounding the tertiary water channels. No or very poor expression in inner mantle, foot muscle, byssal muscle, heart, hepatopancreas, and kidney of Tridacna squamosa kept in darkness for 12 h, immunofluorescent tissue distribution analysis	Tridacna squamosa	-

Substrates and Products (Substrate)

Substrates	Comment Substrates	Organism	Products	Comment (Products)	Rev.	Reac.
H2CO3	-	Tridacna squamosa	CO2 + H2O	-	r

Subunits

Subunits	Comment	Organism
?	x * 66700, about, sequence calculation	Tridacna squamosa

Synonyms

Synonyms	Comment	Organism
DDCA	-	Tridacna squamosa
dual-domain carbonic anhydrase	-	Tridacna squamosa

Expression

Organism	Comment	Expression
Tridacna squamosa	the transcript and protein levels of DDCA/DDCA in the ctenidium of Tridacna squamosa increase significantly after 6 and 12 h of exposure to light, respectively	up

General Information

General Information	Comment	Organism
additional information	the deduced enzyme DDCA sequence contains two distinct alpha-CA domains, each with a specific catalytic site. Each alpha-CA domain of the DDCA has its own set of catalytic and active sites. The first alpha-CA domain comprised the three histidine residues (His116, His118, His141) which coordinate the Zn2+-containing catalytic site, the hydrophobic residues (Val143, Val164, Leu224, Val233, Trp235) that form the CO2 binding pocket, and the gatekeeper residues (Glu128, Thr226). In the first alpha-CA domain, the active binding site for HCO3- and H+ constitutes five hydrophilic residues (Asn85, His87, Gln114, Thr225, and Thr226), of which His87 acts as a proton shuttle for CO2 hydration. Similarly, the Zn2+-containing catalytic site (His391, His393, His416), the hydrophobic residues that form the CO2 binding pocket (Val418, Val439, Leu504, Val513, Trp515), and the gatekeeper residues (Glu403, Thr506) are conserved in the second alpha-CA domain. Unlike the first alpha-CA domain, six hydrophilic residues (Asn361, His363, Gln366, Gln389, Thr505, and Thr506) are found in the second alpha-CA domain, and His363 serves as a proton shuttle for CO2 hydration	Tridacna squamosa
physiological function	the ctenidial DDCA is positioned to dehydrate HCO3- to CO2 in seawater, and to hydrate the CO2 that has permeated the apical membrane back to HCO3- in the cytoplasm. During insolation, the host clam needs to increase the uptake of inorganic carbon from the ambient seawater to benefit the symbiotic zooxanthellae. Only then can the symbionts conduct photosynthesis and share the photosynthates with the host. Enzyme DDCA might participate in the light-enhanced uptake and assimilation of exogenous inorganic carbon	Tridacna squamosa

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Release 2023.1 (January 2023)