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Structure of the carbonic anhydrase VI (CA6) gene: evidence for two distinct groups within the alpha-CA gene family.

ABSTRACT: The secreted carbonic anhydrase (CA VI) is believed to be one of the oldest mammalian CAs in evolutionary terms. To elucidate its gene structure and compare it with other members of the alpha-CA family, we cloned genomic fragments encoding the bovine CA6 gene and determined its exon/intron organization. The gene spans approx. 25 kb and consists of eight exons and seven introns. Exon 1 encodes the 5' untranslated region, the signal peptide and the N-terminus of the mature enzyme. Exon 8 encodes the 3' untranslated region and the C-terminal extension that is unique to CA VI. Exons 2-7 encode the CA domain, which shows significant sequence similarity to other CAs. Two distinct groups exist in the alpha-CA family on the basis of a comparison of the known gene structures. One group consists of the cytoplasmic (CA I, II, III and VII) and mitochondrial (CA V) members. The other group consists of the membrane-bound (CA IV and IX) and secreted (CA VI) members. In particular, the seven exon/intron boundaries in the CA domain of the CA6 gene are conserved in the CA9 gene, which encodes the multidomain protein CA IX that is overexpressed in tumours and has transforming potential.

SUBMITTER: Jiang W

PROVIDER: S-EPMC1220654 | biostudies-other | 1999 Dec

REPOSITORIES: biostudies-other

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The Evolutionary History of Daphniid α-Carbonic Anhydrase within Animalia.

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Project description:Secretory human carbonic anhydrase VI (CA VI) has emerged as a potential drug target due to its role in pathological states, such as excess acidity-caused dental caries and injuries of gastric epithelium. Currently, there are no available CA VI-selective inhibitors or crystallographic structures of inhibitors bound to CA VI. The present study focuses on the site-directed CA II mutant mimicking the active site of CA VI for inhibitor screening. The interactions between CA VI-mimic and a series of benzenesulfonamides were evaluated by fluorescent thermal shift assay, stopped-flow CO2 hydration assay, isothermal titration calorimetry, and X-ray crystallography. Kinetic parameters showed that A65T, N67Q, F130Y, V134Q, L203T mutations did not influence catalytic properties of CA II, but inhibitor affinities resembled CA VI, exhibiting up to 0.16 nM intrinsic affinity for CA VI-mimic. Structurally, binding site of CA VI-mimic was found to be similar to CA VI. The ligand interactions with mutated side chains observed in three crystallographic structures allowed to rationalize observed variation of binding modes and experimental binding affinities to CA VI. This integrative set of kinetic, thermodynamic, and structural data revealed CA VI-mimic as a useful model to design CA VI-specific inhibitors which could be beneficial for novel therapeutic applications.

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Characterization of CA XV, a new GPI-anchored form of carbonic anhydrase.

Project description:The main function of CAs (carbonic anhydrases) is to participate in the regulation of acid-base balance. Although 12 active isoenzymes of this family had already been described, analyses of genomic databases suggested that there still exists another isoenzyme, CA XV. Sequence analyses were performed to identify those species that are likely to have an active form of this enzyme. Eight species had genomic sequences encoding CA XV, in which all the amino acid residues critical for CA activity are present. However, based on the sequence data, it was apparent that CA XV has become a non-processed pseudogene in humans and chimpanzees. RT-PCR (reverse transcriptase PCR) confirmed that humans do not express CA XV. In contrast, RT-PCR and in situ hybridization performed in mice showed positive expression in the kidney, brain and testis. A prediction of the mouse CA XV structure was performed. Phylogenetic analysis showed that mouse CA XV is related to CA IV. Therefore both of these enzymes were expressed in COS-7 cells and studied in parallel experiments. The results showed that CA XV shares several properties with CA IV, i.e. it is a glycosylated glycosylphosphatidylinositol-anchored membrane protein, and it binds CA inhibitor. The catalytic activity of CA XV is low, and the correct formation of disulphide bridges is important for the activity. Both specific and non-specific chaperones increase the production of active enzyme. The results suggest that CA XV is the first member of the alpha-CA gene family that is expressed in several species, but not in humans and chimpanzees.

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