Structure/activity relationships of two alginate lyases from Flavobacterium spp. and their potential application in detergents

Alginate is one of the most abundant marine polysaccharides and is found primarily in brown algae. Enzymes like alginate lyases have been extensively used to depolymerize alginate, breaking the glycosidic bonds through a β-elimination mechanism, and facilitate the utilisation of alginate by algae-associated bacteria to obtain valuable alginate oligosaccharides. Two alginate lyases, Aly40 and Aly30 from the family Polysaccharide Lyase 7 (PL7), were found in a commercial alginate lyase extract from Flavobacterium spp. The species of origin was determined to be Flavobacterium quisquiliarum using proteomics, and both enzymes were expressed in Escherichia coli BL21(DE3) for analysis of their kinetics and substrate specificity. Aly40 is a polyG-specific lyase, whereas Aly30 is a bifunctional lyases active against all the monomeric units of alginate, thus enabling the organism to break down a broad range of alginates. The molecular dynamic simulation of Aly30 in complex with the pentamannuronate indicate the possible dual role of Tyr238 acting as both the Brønsted base and acid to break the scissile β-1,4 glycosidic bond through a syn-β-elimination mechanism. The application of the alginate lyases in detergent was evaluated; Aly40 is a suitable detergent additive and increased stain removal of algal alginate-containing chocolate mousse stains by 52 %, whereas Aly30 did not improve stain removal although could offer other benefits to cleaning compositions by targeting alginates of microbial origin.