Enzymatic properties and the gene structure of a cold-adapted laminarinase from Pseudoalteromonas species LA

We isolated a laminarin-degrading cold-adapted bacterium strain LA from coastal seawater in Sagami Bay, Japan and identified it as a Pseudoalteromonas species. We named the extracellular laminarinase LA-Lam, and purified and characterized it. LA-Lam showed high degradation activity for Laminaria digitata laminarin in the ranges of 15-50°C and pH 5.0-9.0. The major terminal products degraded from L. digitata laminarin with LA-Lam were glucose, laminaribiose, and laminaritriose. The degradation profile of laminarioligosaccharides with LA-Lam suggested that the enzyme has a high substrate binding ability toward tetrameric or larger saccharides. Our results of the gene sequence and the SDS-PAGE analyses revealed that the major part of mature LA-Lam is a catalytic domain that belongs to the GH16 family, although its precursor is composed of a signal peptide, the catalytic domain, and three-repeated unknown regions.