Laminarin, a β-1,3-glucan with occasional β-1,6 branching, is the most abundant source of energy and nutrients in the marine environment. In this study, polysaccharide utilization loci (PULs) for laminarin degradation were identified in various marine Muricauda species, encoding a range of glycoside hydrolases and transglycosylases. In Muricauda lutaonensis ISCAR-4703, the PUL included two GH17 enzymes, separated by a GH30 enzyme and a major facilitator superfamily (MFS) transporter, a feature observed in all corresponding Muricauda PULs. A novel endoacting laminarinase from the PUL, MlGH17A, was characterized and shown to hydrolyze laminarin into laminaribiose, laminaritriose, and laminaritetraose, with laminaritriose as the main product. Bioinformatic analysis showed that the enzyme lacked the typical subdomain found in GH17 plant β-glucanases, leading to a lower number of aglycone subsites (+1 to +3). Instead, MlGH17A possessed more glycone subsites (-1 to -4), attributed to the β3-α3 loop, which was longer than in GH17 plant β-glucanases.
Allahgholi et al. (Mon,) studied this question.