Carb_anhydrase Eukaryotic-type carbonic anhydrase
SMART ACC:	SM001057
Description:	Carbonic anhydrases are zinc metalloenzymes which catalyse the reversible hydration of carbon dioxide to bicarbonate (PUBMED:18336305), (PUBMED:10978542). CAs have essential roles in facilitating the transport of carbon dioxide and protons in the intracellular space, across biological membranes and in the layers of the extracellular space; they are also involved in many other processes, from respiration and photosynthesis in eukaryotes to cyanate degradation in prokaryotes. There are five known evolutionarily distinct CA families (alpha, beta, gamma, delta and epsilon) that have no significant sequence identity and have structurally distinct overall folds. Some CAs are membrane-bound, while others act in the cytosol; there are several related proteins that lack enzymatic activity. The active site of alpha-CAs is well described, consisting of a zinc ion coordinated through 3 histidine residues and a water molecule/hydroxide ion that acts as a potent nucleophile. The enzyme employs a two-step mechanism: in the first step, there is a nucleophilic attack of a zinc-bound hydroxide ion on carbon dioxide; in the second step, the active site is regenerated by the ionisation of the zinc-bound water molecule and the removal of a proton from the active site (PUBMED:9336012). Beta- and gamma-CAs also employ a zinc hydroxide mechanism, although at least some beta-class enzymes do not have water directly coordinated to the metal ion.
InterPro ACC:	IPR001148
InterPro abstract:	This entry represents a domain characteristic of alpha class carbonic anhydrases. The dominating secondary structure is a 10-stranded, twisted β-sheet, which divides the molecules into two halves [ PUBMED:9336012 ]. Alpha-CAs contain a single zinc atom bound to three conserved histidine residues. The catalytically active … expand This entry represents a domain characteristic of alpha class carbonic anhydrases. The dominating secondary structure is a 10-stranded, twisted β-sheet, which divides the molecules into two halves [ PUBMED:9336012 ]. Alpha-CAs contain a single zinc atom bound to three conserved histidine residues. The catalytically active group is the zinc-bound water which ionizes to a hydroxide group. In the mechanism of catalysis, nucleophilic attack of CO2 by a zinc-bound hydroxide ion is followed by displacement of the resulting zinc-bound bicarbonate ion by water; subsequent deprotonation regenerates the nucleophilic zinc-bound hydroxide ion [ PUBMED:8673298 PUBMED:11493685 ]. A carbonic anhydrase-like domain with striking homology to that of the alpha class carbonic anhydrases is also found in receptor-type tyrosine-protein phosphatase gamma and zeta. In this case it may have a different function, as only one of the three His residues that ligate the zinc atom and are required for catalytic activity is conserved [ PUBMED:8382771 ]. Carbonic anhydrases (CA: EC:4.2.1.1 ) are zinc metalloenzymes which catalyse the reversible hydration of carbon dioxide to bicarbonate [ PUBMED:18336305 PUBMED:10978542 ]. The alpha-CAs are found predominantly in animals but also in bacteria and green algae. There are at least 15 isoforms found in mammals, which can be subdivided into cytosolic CAs (CA-I, CA-II, CA-III, CA-VII and CA XIII), mitochondrial CAs (CA-VA and CA-VB), secreted CAs (CA-VI), membrane-associated (CA-IV, CA-IX, CA-XII and CA-XIV) and those without CA activity, the CA-related proteins (CA-RP VIII, X and XI). collapse
Family alignment:	View the Family alignment or the Alignment consensus sequence
There are 15 947 Carb_anhydrase domains in 15 811 proteins in SMART's NRDB database.

Taxonomic distribution of proteins containing Carb_anhydrase domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing Carb_anhydrase domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Predicted cellular role

Cellular role:	Metabolic

Relevant references for this domain

Primary literature for the Carb_anhydrase domain is listed below. Automatically-derived, secondary literature is also available.

KEGG pathways involving proteins which contain this domain

This information is based on the mapping of SMART genomic protein database to KEGG orthologous groups. Percentages are related to the number of proteins containing a Carb_anhydrase domain which could be assigned to a KEGG orthologous group, and not all proteins containing Carb_anhydrase domains. Please note that proteins can be included in multiple pathways, ie. the numbers below will not add to 100%.

KEGG pathways

Some of these pathways are included in the interactive Pathways Explorer overview maps. Select an overview map and click the button below to highlight them in iPath.

KEGG orthologous groups

Some of these KOs are included in the interactive Pathways Explorer overview maps. Select an overview map and click the button below to highlight them in iPath.

3D structures in PDB containing this domain

Links to other resources describing this domain

Pfam	Carb_anhydrase
InterPro	IPR001148