Characterization of beta-1,4-endoglucanase as a polysaccharide-degrading digestive enzyme from disk abalone, Haliotis discus discus

Gene coding for a putative endoglucanase was isolated and characterized from a disk abalone Haliotis discus discus cDNA library and was named as hdEndgI. The full length (1,908 bp) abalone cDNA contained a 1,824 bp open reading frame (ORF), encoding 608 amino acids (aa). The predicted molecular mass and isoelectric point were 65 kDa and 4.5, respectively. The C-terminal region showed conserved catalytic site regions, with the catalytic site residues responsible for the endoglucanase activity. RT–PCR results revealed greater hdEndgI mRNA expression in the hepatopancreas than in the digestive tract, suggesting the key site at which the enzyme is produced. hdEndgI mRNA expression decreased from baseline to the 8th week of starvation in the hepatopancreas; and once re-feeding was initiated, mRNA transcription increased to normal levels within 14 days. This suggests that gene transcription is not totally disturbed due to starvation-induced stress, showing the potential of hdEndgI as a molecular tool for identification of food availability. It further suggests that abalone can survive for 8 weeks without food. The purified hdEndgI recombinant fusion protein was shown to have in vitro activity against carboxymethylcellulose. The enzyme exhibits a broad range of pH stability, the optimal temperature and pH being 40°C and 4.5, respectively.