Abstract
Carbonic anhydrases (CAs) are universal zinc ion containing metalloenzymes that play a pivotal role in various physiological processes. In this study, a CA I (designated as Hdh CA I) was isolated and characterized from the mantle tissue of Pacific abalone, Haliotis discus hannai. The full-length cDNA sequence of Hdh CA I was 1,417-bp in length, encoding a protein of 337 amino acids with molecular weight of 37.58 kDa. Hdh CA I sequence possessed a putative signal peptide of 22 amino acids and a CA catalytic function domain. The predicted protein shared 94 and 78% sequence identities with Haliotis gigantea and Haliotis tuberculata CA I, respectively. Results of phylogenetic analysis indicated that Hdh CA I was evolutionarily close to CA I of H. gigantea and H. tuberculata with high bootstrap values. Significantly higher levels of Hdh CA I mRNA transcript were found in mantle than other examined tissues. In situ hybridization results showed strong hybridization signals in epithelial cells of the dorsal mantle pallial, an area known to synthesize and secrete proteins responsible for the nacreous layer formation of shell. This is the first study on Hdh CA I in H. discus hannai and the results may contribute to further study its physiological functions in shell biomineralization of abalone.
Highlights
Carbonic anhydrases (CAs) are ubiquitous zinc-binding metalloenzymes that regulate acidbase balance through catalyzing a simple physiological reaction: the conversion of CO2 to bicarbonate ions and protons (Lindskog and Silverman, 2000)
Full-length cDNA sequence of CA I was successfully cloned from shell-forming mantle tissue of Pacific abalone, H. discus hannai
A secreted α-type CA was identified from H. discus hannai for the first time, and its mRNA levels in different tissues were analyzed
Summary
Carbonic anhydrases (CAs) are ubiquitous zinc-binding metalloenzymes that regulate acidbase balance through catalyzing a simple physiological reaction: the conversion of CO2 to bicarbonate ions and protons (Lindskog and Silverman, 2000). 16 different α-CA isoforms have been reported based on their catalytic efficacy, molecular signature, kinetic profiles, subcellular localization, and tissue distribution (Nishimori et al, 2007; Alterio et al, 2009). CA VIII, X, and XI isoforms are designated as carbonic anhydrase related proteins (CARPs) owing to the lack of one or more Zn binding histidine residues at the active site (Aspatwar et al, 2010). Most CAs are characterized by the presence of a Zn2+ ion coordinated by three histidine residues except for those in the ζ-CA family, in which zinc is replaced by cadmium (Lane et al, 2005)
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