# Biochemical Characterization of Multimodular Xylanolytic Carbohydrate Esterases from the Marine Bacterium Flavimarina sp. Hel_I_48

## TL;DR

This paper studies three unique enzymes from a marine bacterium that can break down complex sugars, potentially improving biomass utilization for biotechnology.

## Contribution

The study characterizes novel multimodular xylanolytic carbohydrate esterases with unique domain arrangements and bifunctional activities.

## Key findings

- Fl6 combines glucuronyl esterase activity with a carbohydrate binding module.
- Fll1 exhibits xylosidase and acetylxylan esterase activities via a CE3 domain.
- Fll4 is the first enzyme with three CE domains and bifunctional AXE and FAE activities.

## Abstract

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.

Multimodular carbohydrate‐active enzymes often combine different catalytic activities for efficient polysaccharide degradation. In this work, the structural and functional characterization of three multimodular xylan‐targeting esterases, Fl6, Fll1 and Fll4 from Flavimarina sp. Hel_I_48, are presented. Each protein shows novelty in its architecture, with particular emphasis on the enzyme Fll4, which consists of three esterase domains, resulting in bifunctional esterase activity.© 2025 WILEY‐VCH GmbH