Abstract
Alginate, a natural polysaccharide derived from brown seaweed, is finding multiple applications in biomedicine via its transformation through chemical, physical, and, increasingly, enzymatic processes. In this study a novel alginate lyase, AlyDS44, was purified and characterized from a marine actinobacterium, Streptomyces luridiscabiei, which was isolated from decomposing seaweed. The purified enzyme had a specific activity of 108.6 U/mg, with a molecular weight of 28.6 kDa, and was composed of 260 amino acid residues. AlyDS44 is a bifunctional alginate lyase, active on both polyguluronate and polymannuronate, though it preferentially degrades polyguluronate. The optimal pH of this enzyme is 8.5 and the optimal temperature is 45 °C. It is a salt-tolerant alginate lyase with an optimal activity at 0.6 M NaCl. Metal ions Mn2+, Co2+, and Fe2+ increased the alginate degrading activity, but it was inhibited in the presence of Zn2+ and Cu2+. The highly conserved regions of its amino acid sequences indicated that AlyDS44 belongs to the polysaccharide lyase family 7. The main breakdown products of the enzyme on alginate were disaccharides, trisaccharides, and tetrasaccharides, which demonstrated that this enzyme acted as an endo-type alginate lyase. AlyDS44 is a novel enzyme, with the potential for efficient production of alginate oligosaccharides with low degrees of polymerization.
Highlights
Introduction iationsAlginate is the most abundant polysaccharide located in the matrix and in the cell wall of brown seaweed
Eighty strains of marine actinobacteria isolated from decomposing seaweed, including brown, green, and red seaweed, were screened for their ability to grow on bull kelp powder
The alginate lyase gene was composed of 780 bp, encoding 260 amino acid residues
Summary
Alginate is the most abundant polysaccharide located in the matrix and in the cell wall of brown seaweed. It is composed of α-L-guluronate (G) and β-D-mannuronate (M) as the major monomeric units [1]. These units are organized in three different blocks: poly α-L. The number of G and M blocks, as well as the ratio of G to M within alginates, are varied and depend on the sources from which they are isolated. Lee and Mooney [3] summarized the more than 200 different alginates that are currently being manufactured. The structure of alginate is variable, presenting two types of homopolymeric sequences (MM and GG), as well as heteropolymeric sequences (MG and GM) [4]
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