Glucose Modulates Marine Xylanase Activity: Insights From Caulerpa lentillifera and Synthetic β‐1,3‐glucoxylans

Marine xylans are major cell‐wall constituents of green and red algae. While the β‐1,4 and β‐1,3/β‐1,4 mixed‐linkage xylans (MLX) of red algae are homopolymers of xylose, several studies have reported glucose incorporation into green algal β‐1,3‐xylans. However, the consequences of intrachain glucose insertions for the degradation of β‐1,3‐xylan by endo‐acting xylanases remain unknown. Here, high‐performance liquid chromatography coupled with mass spectrometry (HPLC‐MS) analyses demonstrate that glucose is an integral part of di‐ and trisaccharides released from the xylan of green alga Caulerpa lentillifera upon treatment with a β‐1,3‐xylanase and a mixed‐linkage xylanase (MLXase) from marine bacteria. Cleavage patterns on synthetic glucoxylan oligosaccharides generated by automated glycan assembly show that the β‐1,3‐xylanase hydrolyzes the β‐1,3‐bond between glucose and xylose, revealing a previously unrecognized activity within the glycoside hydrolase family 26.