Biochemical Characterization of Multimodular Xylanolytic Carbohydrate Esterases from the Marine Bacterium <i>Flavimarina</i> sp. Hel_I_48

Carbohydrate-active enzymes (CAZymes) are critical for sustainable biomass utilization due to their ability to degrade complex polysaccharides. Frequently, a multimodularity can be observed combining several CAZyme domains and activities in close proximity which can benefit this degradation process. In this study, three multimodular xylanolytic carbohydrate esterases (CEs), named Fl6, Fll1, and Fll4, originating from Flavimarina sp. Hel_I_48 that represent a novel arrangement of catalytic and/or binding domains, are investigated. While Fl6 acts as a glucuronyl esterase, it also contains a carbohydrate binding module which is normally associated with xylanase activity. Fll1 combines xylosidase with acetylxylan esterase (AXE) activity mediated by a CE3 domain. The third enzyme, Fll4, is the first enzyme that comprises three distinct CE domains and shows bifunctional activity as an AXE and a feruloyl esterase (FAE). Investigation of the single domains reveals that the CE6 domain of Fll4 mediates its AXE activity while one of the putative CE1 domains, CE1a, mediates the FAE activity. This investigation of multimodularity of marine CAZymes not only enhances our understanding of these enzymes but may provide a promising route toward more efficient algal biomass utilization for biotechnological applications.