Structure and function of a glycoside hydrolase family 8 endoxylanase from Teredinibacter turnerae

The biological conversion of lignocellulosic matter into high‐value chemicals or biofuels is of increasing industrial importance as the sector slowly transitions away from nonrenewable sources. Many industrial processes involve the use of cellulolytic enzyme cocktails – a selection of glycoside hydrolases and, increasingly, polysaccharide oxygenases – to break down recalcitrant plant polysaccharides. ORFs from the genome of Teredinibacter turnerae , a symbiont hosted within the gills of marine shipworms, were identified in order to search for enzymes with desirable traits. Here, a putative T. turnerae glycoside hydrolase from family 8, hereafter referred to as TtGH8, is analysed. The enzyme is shown to be active against β‐1,4‐xylan and mixed‐linkage (β‐1,3,β‐1,4) marine xylan. Kinetic parameters, obtained using high‐performance anion‐exchange chromatography with pulsed amperometric detection and 3,5‐dinitrosalicyclic acid reducing‐sugar assays, show that TtGH8 catalyses the hydrolysis of β‐1,4‐xylohexaose with a k cat / K m of 7.5 × 10 7   M −1  min −1 but displays maximal activity against mixed‐linkage polymeric xylans, hinting at a primary role in the degradation of marine polysaccharides. The three‐dimensional structure of TtGH8 was solved in uncomplexed and xylobiose‐, xylotriose‐ and xylohexaose‐bound forms at approximately 1.5 Å resolution; the latter was consistent with the greater k cat / K m for hexasaccharide substrates. A 2,5 B boat conformation observed in the −1 position of bound xylotriose is consistent with the proposed conformational itinerary for this class of enzyme. This work shows TtGH8 to be effective at the degradation of xylan‐based substrates, notably marine xylan, further exemplifying the potential of T. turnerae for effective and diverse biomass degradation.