Molecular characterization, gene expression analysis and biochemical properties of α-amylase from the disk abalone, Haliotis discus discus

The present study reports the molecular characterization, cloning, expression, and biochemical characterization of α-amylase identified from the disk abalone, Haliotis discus discus cDNA library. The full length of the α-amylase cDNA was 1650 bp, and it encoded a polypeptide of 511 amino acids. The predicted HdAmyI molecular mass of mature protein was 54 kDa and the estimated isoelectric point (pI) was 8.3. The α-amylase gene showed its characteristic motifs, catalytic sites, substrate binding sites and conserved regions with other known species of α-amylases. Purified recombinant HdAmyI exhibited a relatively low activity of 0.1 U/mg protein towards 1% starch. HdAmyI had an optimum temperature and pH of 50 °C and 6.5, respectively. It also demonstrated stability in a wide range of temperatures and pH. Tissue-specific mRNA expression results showed that HdAmyI is expressed only in the digestive tract and hepatopancreas, with the highest levels in the hepatopancreas. Over 8 weeks of starvation, α-amylase transcription was decreased significantly relative to basal levels. However, after starvation, mRNA transcription was increased and returned to normal level by the 2nd week of feeding, suggesting that the α-amylase mRNA expression changes according to variations in food availability at the transcriptional level in disk abalone.