Abstract
A novel cold-adapted and salt-tolerant α-amylase gene (amy175) from Antarctic sea ice bacterium Pseudoalteromonas sp. M175 was successfully cloned and expressed. The open reading frame (ORF) of amy175 had 1722 bp encoding a protein of 573 amino acids residues. Multiple alignments indicated Amy175 had seven highly conserved sequences and the putative catalytic triad (Asp244, Glu286, and Asp372). It was the first identified member of GH13_36 subfamily which contained QPDLN in the CSR V. The recombinant enzyme (Amy175) was purified to homogeneity with a molecular mass of about 62 kDa on SDS-PAGE. It had a mixed enzyme specificity of α-amylase and α-glucosidase. Amy175 displayed highest activity at pH 8.0 and 25°C and exhibited extreme salt-resistance with the maximum activity at 1 M NaCl. Amy175 was strongly stimulated by Mg2+, Ni2+, K+, 1 mM Ca2+, 1 mM Ba2+, 1 mM Pb2+, 1 mM sodium dodecyl sulphate (SDS), and 10% dimethyl sulfoxide (DMSO) but was significantly inhibited by Cu2+, Mn2+, Hg2+, 10 mM β-mercaptoethanol (β-ME), and 10% Tween 80. Amy175 demonstrated excellent resistance towards all the tested commercial detergents, and wash performance analysis displayed that the addition of Amy175 improved the stain removal efficiency. This study demonstrated that Amy175 would be proposed as a novel α-amylase source for industrial application in the future.
Highlights
Introduction αAmylases (E.C.3.2.1.1) are hydrolytic enzymes which can randomly cleave α-1,4-glycosidic linkages in starch molecules to generate gradually smaller polymers consisting of glucose units [1, 2]
Most α-amylases belong to glycoside hydrolase family 13 (GH13)
M175. amy175 encodes a protein of 573 amino acids, which contains a predicted Nterminal signal peptide comprising 23 amino acids and a mature α-amylase (Amy175) with a calculated molecular weight of 62.4 kDa and pI of 4.9
Summary
Amylases (E.C.3.2.1.1) are hydrolytic enzymes which can randomly cleave α-1,4-glycosidic linkages in starch molecules to generate gradually smaller polymers consisting of glucose units [1, 2]. Most α-amylases belong to glycoside hydrolase family 13 (GH13). Among classification systems of glycoside hydrolases (GHs), the family GH13 forms the clan GH-H together with the families 70 and 77 [6]. As the largest GH family, the family GH13 consists of more than 30 different enzyme specificities and more than 55,500 sequences (http://www.cazy.org/GH13.html). It was officially divided into 35 subfamilies by the CAZy curators in 2006 [8]. The overall sequences of family GH13 members own very low identity, they possess 4-7 conserved sequence regions (CSRs) and a catalytic triad (Asp, Glu, and Asp) [11, 12]
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