Characterisation of novel lignocellulosic enzymes from the shipworm symbiont Teredinibacter turnerae

Biomass is a renewable resource which can be broken down into bio-derived high value molecules using industrial processing, parts of which rely on enzymatic degradation. Nature provides a vast pool of highly efficient lignocellulosic enzymes capable of breaking down the multitude of natural polymers found in biomass. Identifying organisms that thrive within ecological niches based around the consumption of lignocellulosic material is likely to yield novel biomass degrading enzymes. Shipworms are marine organisms which use shell-like protrusions to burrow into submerged wooden substrates in oceanic environments. Endosymbiotic bacteria, Teredinibacter turnerae, found within the gills of the shipworm is thought to provide the host with a variety of carbohydrate active enzymes for use in the digestion. This work characterises carbohydrate active enzymes identified within the genome of T. turnerae including glycoside hydrolases (GH) from families 5, 8 and 12 as well as a lytic polysaccharide monooxygenase (LPMO) from subfamily AA10. Analysis of three GH5 proteins found activities on cellulose (TtGH5_2 and TtGH5_un) and xyloglucan (TtGH5_4), with one protein (TtGH5_un) likely representing a new GH5 subfamily. TtGH8 was found to be highly active on xylans, with kinetics and structural studies showing a preference for longer xylooligosaccharides. The molecular structure of TtGH12 was solved, but substrate specificity remains unknown, indicating a potentially new activity subclass within the GH12 family. TtAA10 was active on crystalline cellulose through copper mediated oxidative attack at C1 or C4 either side of the glycosidic bond, and modelled structurally at high resolution. Like many other specialised organisms, the genome of T. turnerae is a treasure chest full of potentially useful lignocellulose degrading proteins. This work has assessed the activity and structure of several enzymes from T. turnerae and found multiple different substrate activities and potentially novel functions, paving the way for further experimentation and potential utilisation in industry.