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.