Characterization of a new endo-type alginate lyase from Vibrio sp. NJU-03

A gene, encoding a new alginate lyase AlgNJU-03, was cloned from marine bacteria Vibrio sp. NJU-03. The recombinant alginate lyase was characterized followed by being purified by NTA-Ni Sepharose. It exhibited the highest activity (6468.99 U/mg) at pH 7.0 and 30 °C. Interestingly, AlgNJU-03 possessed broader substrate specificity and high activity toward both polyM (poly β-D-mannuronate) and polyG (poly α-L-guluronate), indicating that it is a bifunctional alginate lyase. Furthermore, K_m of AlgNJU-03toward polyG (4.00 mM) is lower than those toward alginate (8.50 mM) and polyM (10.94 mM), demonstrating that the enzyme has a higher affinity to polyG. Meanwhile, the catalytic efficiency (K_cat/K_m) toward polyG (11.47 s⁻¹/mM) is much higher than those toward sodium alginate (3.60 s⁻¹/mM) and polyM (0.50 s⁻¹/mM). ESI–MS analysis suggested that AlgNJU-03 mainly released disaccharides, trisaccharides and tetrasaccharides from the three kinds of substrates in an endolytic manner. Therefore, it may be a potential tool to produce alginate oligosaccharides with low DP.