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Abstract

Xylophagous longhorned beetles thrive in challenging environments. To access nutrients, they secrete plant-cell-wall-degrading enzymes in their gut fluid, among them, cellulases of the subfamily 2 of glycoside hydrolase family 5 (GH5\_2). Recently, we discovered that several beetle-derived GH5\_2s use xylan as a substrate instead of cellulose, which is unusual for this family of enzymes. Here, we analyze the substrate specificity of a GH5\_2 xylanase from the beetle Apriona japonica (AJAGH5\_2-1) using commercially available substrates and synthetic arabinoxylan oligo- and polysaccharides. We demonstrate that AJAGH5\_2-1 deals with arabinoxylan polysaccharides in a way that is distinct from classical xylanase families like GH10 and GH11. AJAGH5\_2-1 is active on long oligosaccharides and cleaves at the non-reducing end of a substituted xylose residue (position +1) only if (i) three xylose residues are present upstream and downstream of the cleavage site and (ii) xylose residues at positions -1, -2, +2 and +3 are not substituted.