Cloning, characterization, and inhibition of the novel ß-carbonic anhydrase from parasitic blood fluke, Schistosoma mansoni.

Schistosoma mansoni is an intestinal parasite with one ß-class carbonic anhydrase, SmaBCA. We report the sequence enhancing, production, catalytic activity, and inhibition results of the recombinant SmaBCA. It showed significant catalytic activity on CO2 hydration in vitro with kcat 1.38 × 105 s-1 and kcat/Km 2.33 × 107 M-1 s-1. Several sulphonamide inhibitors, from which many are clinically used, showed submicromolar or nanomolar inhibitory effects on SmaBCA. The most efficient inhibitor with a KI of 43.8 nM was 4-(2-amino-pyrimidine-4-yl)-benzenesulfonamide. Other effective inhibitors with KIs in the range of 79.4-95.9 nM were benzolamide, brinzolamide, topiramate, dorzolamide, saccharin, epacadostat, celecoxib, and famotidine. The other tested compounds showed at least micromolar range inhibition against SmaBCA. Our results introduce SmaBCA as a novel target for drug development against schistosomiasis, a highly prevalent parasitic disease.

Biochemical and Biophysical Characterization of Carbonic Anhydrase VI from Human Milk and Saliva.

Carbonic anhydrases (CA, EC 4.2.1.1) catalyze the hydration of carbon dioxide and take part in many essential physiological processes. In humans, 15 CAs are characterized, including the only secreted isoenzyme CA VI. CA VI has been linked to specific processes in the mouth, namely bitter taste perception, dental caries, and maintenance of enamel pellicle, and implicated in several immunity-related phenomena. However, little is known of the mechanisms of the above. In this study, we characterized human CA VI purified from saliva and milk with biophysical methods and measured their enzyme activities and acetazolamide inhibition. Size-exclusion chromatography showed peaks of salivary and milk CA VI corresponding to hexameric state or larger at pH 7.5. At pH 5.0 the hexamer peaks dominated. SDS- PAGE of milk CA VI protein treated with a bifunctional crosslinker further confirmed that a majority of CA VI is oligomers of similar sizes in solution. Mass spectrometry experiments confirmed that both of the two putative N-glycosylation sites, Asn67 and Asn256, are heterogeneously glycosylated. The attached glycans in milk CA VI were di- and triantennary complex-type glycans, carrying both a core fucose and 1 to 2 additional fucose units, whereas the glycans in salivary CA VI were smaller, seemingly degraded forms of core fucosylated complex- or hybrid-type glycans. Mass spectrometry also verified the predicted signal peptide cleavage site and the terminal residue, Gln 18, being in pyroglutamate form. Thorough characterization of CA VI paves way to better understanding of the biological function of the protein.

Cloning, purification, kinetic and anion inhibition studies of a recombinant ß-carbonic anhydrase from the Atlantic salmon parasite platyhelminth Gyrodactylus salaris.

A ß-class carbonic anhydrase (CA, EC 4.2.1.1) was cloned from the genome of the Monogenean platyhelminth Gyrodactylus salaris, a parasite of Atlantic salmon. The new enzyme, GsaCAß has a significant catalytic activity for the physiological reaction, CO2 + H2O ⇋ HCO3- + H+ with a kcat of 1.1 × 105 s-1 and a kcat/Km of 7.58 × 106 M-1 × s-1. This activity was inhibited by acetazolamide (KI of 0.46 µM), a sulphonamide in clinical use, as well as by selected inorganic anions and small molecules. Most tested anions inhibited GsaCAß at millimolar concentrations, but sulfamide (KI of 81 µM), N,N-diethyldithiocarbamate (KI of 67 µM) and sulphamic acid (KI of 6.2 µM) showed a rather efficient inhibitory action. There are currently very few non-toxic agents effective in combating this parasite. GsaCAß is subsequently proposed as a new drug target for which effective inhibitors can be designed.

Carbonic anhydrases in metazoan model organisms: molecules, mechanisms, and physiology.

During the past three decades, mice, zebrafish, fruit flies, and Caenorhabditis elegans have been the primary model organisms used for the study of various biological phenomena. These models have also been adopted and developed to investigate the physiological roles of carbonic anhydrases (CAs) and carbonic anhydrase-related proteins (CARPs). These proteins belong to eight CA families and are identified by Greek letters: α, ß, γ, δ, ζ, η, θ, and ι. Studies using model organisms have focused on two CA families, α-CAs and ß-CAs, which are expressed in both prokaryotic and eukaryotic organisms with species-specific distribution patterns and unique functions. This review covers the biological roles of CAs and CARPs in light of investigations performed in model organisms. Functional studies demonstrate that CAs are not only linked to the regulation of pH homeostasis, the classical role of CAs, but also contribute to a plethora of previously undescribed functions.

Neural Network and Random Forest Models in Protein Function Prediction.

Over the past decade, the demand for automated protein function prediction has increased due to the volume of newly sequenced proteins. In this paper, we address the function prediction task by developing an ensemble system automatically assigning Gene Ontology (GO) terms to the given input protein sequence. We develop an ensemble system which combines the GO predictions made by random forest (RF) and neural network (NN) classifiers. Both RF and NN models rely on features derived from BLAST sequence alignments, taxonomy and protein signature analysis tools. In addition, we report on experiments with a NN model that directly analyzes the amino acid sequence as its sole input, using a convolutional layer. The Swiss-Prot database is used as the training and evaluation data. In the CAFA3 evaluation, which relies on experimental verification of the functional predictions, our submitted ensemble model demonstrates competitive performance ranking among top-10 best-performing systems out of over 100 submitted systems. In this paper, we evaluate and further improve the CAFA3-submitted system. Our machine learning models together with the data pre-processing and feature generation tools are publicly available as an open source software at https://github.com/TurkuNLP/CAFA3.

Engineered Carbonic Anhydrase VI-Mimic Enzyme Switched the Structure and Affinities of Inhibitors.

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.

Catalytically inactive carbonic anhydrase-related proteins enhance transport of lactate by MCT1.

Carbonic anhydrases (CA) catalyze the reversible hydration of CO2 to protons and bicarbonate and thereby play a fundamental role in the epithelial acid/base transport mechanisms serving fluid secretion and absorption for whole-body acid/base regulation. The three carbonic anhydrase-related proteins (CARPs) VIII, X, and XI, however, are catalytically inactive. Previous work has shown that some CA isoforms noncatalytically enhance lactate transport through various monocarboxylate transporters (MCT). Therefore, we examined whether the catalytically inactive CARPs play a role in lactate transport. Here, we report that CARP VIII, X, and XI enhance transport activity of the MCT MCT1 when coexpressed in Xenopus oocytes, as evidenced by the rate of rise in intracellular H+ concentration detected using ion-sensitive microelectrodes. Based on previous studies, we suggest that CARPs may function as a 'proton antenna' for MCT1, to drive proton-coupled lactate transport across the cell membrane.

Herbal Drug use in Sickle Cell Disease Management; Trends and Perspectives in Sub-Saharan Africa - A Systematic Review.

INTRODUCTION: Nigeria has the largest burden of Sickle Cell Disease (SCD) with estimated 100,000 new born affected annually. SCD is a Hemoglobin (Hb) disorder with the major form resulting from the substitution of a polar glutamate (Glu) by non-polar Valine (Val) in an invariant region of Hbß chain-subunit. Species of Hb found in the sickle cell trait are HbA and HbS in a 60:40 proportion, in SCD only HbS, in the HbC disease only HbC, and in the SC disease it's HbS and HbC in a 50:50 equal proportion. OBJECTIVE: This paper reviews herbal medicines usage in sub-Saharan Africa (sSA) to ameliorate the crisis associated with SCD. The model Hb tetramer suggests a higher membrane affinity of HbS and HbC, promoting dehydration of RBCs, with concomitant in vivo crystallization. Some drawbacks using these herbal drugs include; poor bioavailability and the lack of proper pharmacovigilance monitoring procedures arising from weak governance structure combined with under reporting of herbal usage to physicians were discussed. Probable epigenetic loci that could be targeted using phytomedicines for effective SCD management were also discussed. METHODS: Using search engines, several databases including Google scholar, PubMed, Academic Resource Index were utilized as a source for relevant publications/ literature. The protein coordinates for the Hb tetramer were obtained from the Protein Data Bank (PDB). CONCLUSION: Manipulation of epigenetics to achieve better SCD management involves careful thinking. Herein, we discuss some epigenetic interactions that could be putatively tweaked with a view of enhancing soluble bioactive small molecular components with the potential to reactivate γ -globin genes, thereby boosting immune response in patient with SCD.

Identification and characterization of a novel zebrafish (Danio rerio) pentraxin-carbonic anhydrase.

BACKGROUND: Carbonic anhydrases (CAs) are ubiquitous, essential enzymes which catalyze the conversion of carbon dioxide and water to bicarbonate and H+ ions. Vertebrate genomes generally contain gene loci for 15-21 different CA isoforms, three of which are enzymatically inactive. CA VI is the only secretory protein of the enzymatically active isoforms. We discovered that non-mammalian CA VI contains a C-terminal pentraxin (PTX) domain, a novel combination for both CAs and PTXs. METHODS: We isolated and sequenced zebrafish (Danio rerio) CA VI cDNA, complete with the sequence coding for the PTX domain, and produced the recombinant CA VI-PTX protein. Enzymatic activity and kinetic parameters were measured with a stopped-flow instrument. Mass spectrometry, analytical gel filtration and dynamic light scattering were used for biophysical characterization. Sequence analyses and Bayesian phylogenetics were used in generating hypotheses of protein structure and CA VI gene evolution. A CA VI-PTX antiserum was produced, and the expression of CA VI protein was studied by immunohistochemistry. A knock-down zebrafish model was constructed, and larvae were observed up to five days post-fertilization (dpf). The expression of ca6 mRNA was quantitated by qRT-PCR in different developmental times in morphant and wild-type larvae and in different adult fish tissues. Finally, the swimming behavior of the morphant fish was compared to that of wild-type fish. RESULTS: The recombinant enzyme has a very high carbonate dehydratase activity. Sequencing confirms a 530-residue protein identical to one of the predicted proteins in the Ensembl database (ensembl.org). The protein is pentameric in solution, as studied by gel filtration and light scattering, presumably joined by the PTX domains. Mass spectrometry confirms the predicted signal peptide cleavage and disulfides, and N-glycosylation in two of the four observed glycosylation motifs. Molecular modeling of the pentamer is consistent with the modifications observed in mass spectrometry. Phylogenetics and sequence analyses provide a consistent hypothesis of the evolutionary history of domains associated with CA VI in mammals and non-mammals. Briefly, the evidence suggests that ancestral CA VI was a transmembrane protein, the exon coding for the cytoplasmic domain was replaced by one coding for PTX domain, and finally, in the therian lineage, the PTX-coding exon was lost. We knocked down CA VI expression in zebrafish embryos with antisense morpholino oligonucleotides, resulting in phenotype features of decreased buoyancy and swim bladder deflation in 4 dpf larvae. DISCUSSION: These findings provide novel insights into the evolution, structure, and function of this unique CA form.

Horizontal transfer of ß-carbonic anhydrase genes from prokaryotes to protozoans, insects, and nematodes.

BACKGROUND: Horizontal gene transfer (HGT) is a movement of genetic information occurring outside of normal mating activities. It is especially common between prokaryotic endosymbionts and their protozoan, insect, and nematode hosts. Although beta carbonic anhydrase (ß-CA) plays a crucial role in metabolic functions of many living organisms, the origin of ß-CA genes in eukaryotic species remains unclear. METHODS: This study was conducted using phylogenetics, prediction of subcellular localization, and identification of ß-CA, transposase, integrase, and resolvase genes on the MGEs of bacteria. We also structurally analyzed ß-CAs from protozoans, insects, and nematodes and their putative prokaryotic common ancestors, by homology modelling. RESULTS: Our investigations of a number of target genomes revealed that genes coding for transposase, integrase, resolvase, and conjugation complex proteins have been integrated with ß-CA gene sequences on mobile genetic elements (MGEs) which have facilitated the mobility of ß-CA genes from bacteria to protozoan, insect, and nematode species. The prokaryotic origin of protozoan, insect, and nematode ß-CA enzymes is supported by phylogenetic analyses, prediction of subcellular localization, and homology modelling. CONCLUSION: MGEs form a complete set of enzymatic tools, which are relevant to HGT of ß-CA gene sequences from prokaryotes to protozoans, insects, and nematodes.

Inactivation of ca10a and ca10b Genes Leads to Abnormal Embryonic Development and Alters Movement Pattern in Zebrafish.

Carbonic anhydrase related proteins (CARPs) X and XI are highly conserved across species and are predominantly expressed in neural tissues. The biological role of these proteins is still an enigma. Ray-finned fish have lost the CA11 gene, but instead possess two co-orthologs of CA10. We analyzed the expression pattern of zebrafish ca10a and ca10b genes during embryonic development and in different adult tissues, and studied 61 CARP X/XI-like sequences to evaluate their phylogenetic relationship. Sequence analysis of zebrafish ca10a and ca10b reveals strongly predicted signal peptides, N-glycosylation sites, and a potential disulfide, all of which are conserved, suggesting that all of CARP X and XI are secretory proteins and potentially dimeric. RT-qPCR showed that zebrafish ca10a and ca10b genes are expressed in the brain and several other tissues throughout the development of zebrafish. Antisense morpholino mediated knockdown of ca10a and ca10b showed developmental delay with a high rate of mortality in larvae. Zebrafish morphants showed curved body, pericardial edema, and abnormalities in the head and eye, and there was increased apoptotic cell death in the brain region. Swim pattern showed abnormal movement in morphant zebrafish larvae compared to the wild type larvae. The developmental phenotypes of the ca10a and ca10b morphants were confirmed by inactivating these genes with the CRISPR/Cas9 system. In conclusion, we introduce a novel zebrafish model to investigate the mechanisms of CARP Xa and CARP Xb functions. Our data indicate that CARP Xa and CARP Xb have important roles in zebrafish development and suppression of ca10a and ca10b expression in zebrafish larvae leads to a movement disorder.

The ß-carbonic anhydrase from the malaria mosquito Anopheles gambiae is highly inhibited by sulfonamides.

A ß-carbonic anhydrase (CA, EC 4.2.1.1) was cloned, purified and characterized from Anopheles gambiae, the mosquito species mainly involved in the transmission of malaria. The new enzyme, AgaCA, showed a significant catalytic activity for the physiologic reaction, CO2 hydration to bicarbonate and protons, with a kcat of 7.2×10(5)s(-1) and kcat/Km of 5.6×10(7)M(-1)s(-1), being thus similar to parasite ß-CAs which were discovered earlier as drug targets for antifungal or anti-protozoan agents. An inhibition study of AgaCA with a panel of aromatic, aliphatic and heterocyclic sulfonamides allowed us to identify several low nanomolar inhibitors of the enzyme. Benzolamide and aminobenzolamide showed inhibition constants of 6.8-9.8nM, whereas a structurally related aromatic derivative, 4-(2-hydroxymethyl-4-nitrophenyl-sulfonamidoethyl)-benzenesulfonamide was the strongest inhibitor with a KI of 6.1nM. As ß-CAs are not present in mammals, including humans, finding effective and selective A. gambiae CA inhibitors may lead to alternative procedures for controlling malaria by impairing the growth of its transmission vector, the mosquito.

Beta carbonic anhydrases: novel targets for pesticides and anti-parasitic agents in agriculture and livestock husbandry.

BACKGROUND: The genomes of many insect and parasite species contain beta carbonic anhydrase (ß-CA) protein coding sequences. The lack of ß-CA proteins in mammals makes them interesting target proteins for inhibition in treatment of some infectious diseases and pests. Many insects and parasites represent important pests for agriculture and cause enormous economic damage worldwide. Meanwhile, pollution of the environment by old pesticides, emergence of strains resistant to them, and their off-target effects are major challenges for agriculture and society. METHODS: In this study, we analyzed a multiple sequence alignment of 31 ß-CAs from insects, some parasites, and selected plant species relevant to agriculture and livestock husbandry. Using bioinformatics tools a phylogenetic tree was generated and the subcellular localizations and antigenic sites of each protein were predicted. Structural models for ß-CAs of Ancylostoma caninum, Ascaris suum, Trichinella spiralis, and Entamoeba histolytica, were built using Pisum sativum and Mycobacterium tuberculosis ß-CAs as templates. RESULTS: Six ß-CAs of insects and parasites and six ß-CAs of plants are predicted to be mitochondrial and chloroplastic, respectively, and thus may be involved in important metabolic functions. All 31 sequences showed the presence of the highly conserved ß-CA active site sequence motifs, CXDXR and HXXC (C: cysteine, D: aspartic acid, R: arginine, H: histidine, X: any residue). We discovered that these two motifs are more antigenic than others. Homology models suggested that these motifs are mostly buried and thus not well accessible for recognition by antibodies. CONCLUSIONS: The predicted mitochondrial localization of several ß-CAs and hidden antigenic epitopes within the protein molecule, suggest that they may not be considered major targets for vaccines. Instead, they are promising candidate enzymes for small-molecule inhibitors which can easily penetrate the cell membrane. Based on current knowledge, we conclude that ß-CAs are potential targets for development of small molecule pesticides or anti-parasitic agents with minimal side effects on vertebrates.

Bioinformatic analysis of beta carbonic anhydrase sequences from protozoans and metazoans.

BACKGROUND: Despite the high prevalence of parasitic infections, and their impact on global health and economy, the number of drugs available to treat them is extremely limited. As a result, the potential consequences of large-scale resistance to any existing drugs are a major concern. A number of recent investigations have focused on the effects of potential chemical inhibitors on bacterial and fungal carbonic anhydrases. Among the five classes of carbonic anhydrases (alpha, beta, gamma, delta and zeta), beta carbonic anhydrases have been reported in most species of bacteria, yeasts, algae, plants, and particular invertebrates (nematodes and insects). To date, there has been a lack of knowledge on the expression and molecular structure of beta carbonic anhydrases in metazoan (nematodes and arthropods) and protozoan species. METHODS: Here, the identification of novel beta carbonic anhydrases was based on the presence of the highly-conserved amino acid sequence patterns of the active site. A phylogenetic tree was constructed based on codon-aligned DNA sequences. Subcellular localization prediction for each identified invertebrate beta carbonic anhydrase was performed using the TargetP webserver. RESULTS: We verified a total of 75 beta carbonic anhydrase sequences in metazoan and protozoan species by proteome-wide searches and multiple sequence alignment. Of these, 52 were novel, and contained highly conserved amino acid residues, which are inferred to form the active site in beta carbonic anhydrases. Mitochondrial targeting peptide analysis revealed that 31 enzymes are predicted with mitochondrial localization; one was predicted to be a secretory enzyme, and the other 43 were predicted to have other undefined cellular localizations. CONCLUSIONS: These investigations identified 75 beta carbonic anhydrases in metazoan and protozoan species, and among them there were 52 novel sequences that were not previously annotated as beta carbonic anhydrases. Our results will not only change the current information in proteomics and genomics databases, but will also suggest novel targets for drugs against parasites.

Carbonic anhydrase related proteins: molecular biology and evolution.

The catalytically inactive isoforms of α-carbonic anhydrases are known as carbonic anhydrase related proteins (CARPs). The CARPs occur independently or as domains of other proteins in animals (both vertebrates and invertebrates) and viruses. The catalytic inactivity of CARPs is due to the lack of histidine residues required for the coordination of the zinc atom. The phylogenetic analysis shows that these proteins are highly conserved across the species. The three CARPs in vertebrates are known as CARP VIII, X and XI. CARPs orthologous to CARP VIII are found in deuterostome invertebrates, whereas protostomes only possess orthologs of CARP X. The CA-like domains of receptor-type protein tyrosine phosphatases (PTPR) are found only in PTPRG and PTPRZ. Most of these CARPs are predominantly expressed in central nervous system. Among the three vertebrate CA isoforms, CARP VIII is functionally associated with motor coordination in human, mouse and zebrafish and certain types of cancers in humans. Vertebrate expression studies show that CARP X is exclusively expressed in the brain. CARP XI is only found in tetrapods and is highly expressed in the central nervous system (CNS) of humans and mice and is also associated with several cancers. CARP VIII, PTPRZ and PTPRG have been shown to coordinate the function of other proteins by protein-protein interaction, and viral CARPs participate in attachment to host cells, but the precise biological function of CARPs X and XI is still unknown. The findings so far suggest many novel functions for the CARP subfamily, most likely related to binding to other proteins.

Cloning, characterization, and sulfonamide and thiol inhibition studies of an α-carbonic anhydrase from Trypanosoma cruzi, the causative agent of Chagas disease.

An α-carbonic anhydrase (CA, EC 4.2.1.1) has been identified, cloned, and characterized from the unicellular protozoan Trypanosoma cruzi, the causative agent of Chagas disease. The enzyme (TcCA) has a very high catalytic activity for the CO2 hydration reaction, being similar kinetically to the human (h) isoform hCA II, although it is devoid of the His64 proton shuttle. A large number of aromatic/heterocyclic sulfonamides and some 5-mercapto-1,3,4-thiadiazoles were investigated as TcCA inhibitors. The aromatic sulfonamides were weak inhibitors (K(I) values of 192 nM to 84 µM), whereas some heterocyclic compounds inhibited the enzyme with K(I) values in the range 61.6-93.6 nM. The thiols were the most potent in vitro inhibitors (K(I) values of 21.1-79.0 nM), and some of them also inhibited the epimastigotes growth of two T. cruzi strains in vivo.

An update on carbonic anhydrase-related proteins VIII, X and XI.

The catalytically inactive isoforms of carbonic anhydrase (CAs) are known as CA-related proteins (CARPs) VIII, X, and XI. They have highly conserved amino acid sequences. These proteins are predominantly expressed in human and mouse brain, however, their precise roles are poorly known. CARP VIII is functionally associated with motor coordination in human and mouse. CARP X is more highly expressed in the pineal gland during night compared to the day time, suggesting a function for wake/sleep patterns. Phylogeny shows that CARP XI has emerged from CARP X. It is only found in tetrapods and is highly expressed in the central nervous system (CNS) of humans and is also associated with several cancers. Detailed analysis of CARPs is in progress in our laboratory to understand their role in normal physiology. We present a review of literature on CARPs and present some novel data on CARPs obtained in our laboratory.

Characterization, bioinformatic analysis and dithiocarbamate inhibition studies of two new α-carbonic anhydrases, CAH1 and CAH2, from the fruit fly Drosophila melanogaster.

Carbonic anhydrases (CAs) are essential and ubiquitous enzymes. Thus far, there are no articles on characterization of Drosophila melanogaster α-CAs. Data from invertebrate CA studies may provide opportunities for anti-parasitic drug development because α-CAs are found in many parasite or parasite vector invertebrates. We have expressed and purified D. melanogaster CAH1 and CAH2 as proteins of molecular weights 30kDa and 28kDa. CAH1 is cytoplasmic whereas CAH2 is a membrane-attached protein. Both are highly active enzymes for the CO2 hydration reaction, being efficiently inhibited by acetazolamide. CAH2 in the eye of D. melanogaster may provide a new animal model for CA-related eye diseases. A series of dithiocarbamates were also screened as inhibitors of these enzymes, with some representatives showing inhibition in the low nanomolar range.

Abnormal cerebellar development and ataxia in CARP VIII morphant zebrafish.

Congenital ataxia and mental retardation are mainly caused by variations in the genes that affect brain development. Recent reports have shown that mutations in the CA8 gene are associated with mental retardation and ataxia in humans and ataxia in mice. The gene product, carbonic anhydrase-related protein VIII (CARP VIII), is predominantly present in cerebellar Purkinje cells, where it interacts with the inositol 1,4,5-trisphosphate receptor type 1, a calcium channel. In this study, we investigated the effects of the loss of function of CARP VIII during embryonic development in zebrafish using antisense morpholino oligonucleotides against the CA8 gene. Knockdown of CA8 in zebrafish larvae resulted in a curved body axis, pericardial edema and abnormal movement patterns. Histologic examination revealed gross morphologic defects in the cerebellar region and in the muscle. Electron microscopy studies showed increased neuronal cell death in developing larvae injected with CA8 antisense morpholinos. These data suggest a pivotal role for CARP VIII during embryonic development. Furthermore, suppression of CA8 expression leads to defects in motor and coordination functions, mimicking the ataxic human phenotype. This work reveals an evolutionarily conserved function of CARP VIII in brain development and introduces a novel zebrafish model in which to investigate the mechanisms of CARP VIII-related ataxia and mental retardation in humans.

Analysis of evolution of carbonic anhydrases IV and XV reveals a rich history of gene duplications and a new group of isozymes.

Carbonic anhydrase (CA) isozymes CA IV and CA XV are anchored on the extracellular cell surface via glycosylphosphatidylinositol (GPI) linkage. Analysis of evolution of these isozymes in vertebrates reveals an additional group of GPI-linked CAs, CA XVII, which has been lost in mammals. Our work resolves nomenclature issues in GPI-linked fish CAs. Review of expression data brings forth previously unreported tissue and cancer types in which human CA IV is expressed. Analysis of collective glycosylation patterns of GPI-linked CAs suggests functionally important regions on the protein surface.