Structural and Catalytic Characterization of β-1,3-Glucan Synthases of Mushroom Ganoderma lucidum.

β-Glucans are regarded as the key contributors to nutritional and supplementary credits of well-known edible/medicinal mushroom Ganoderma lucidum. However, the biosynthesis pathways of β-glucans and the involved key enzymes/genes in G. lucidum are still not well investigated. The present study cloned and bioinformatically analyzed a 5259-bp gene GLGLS1 and a 5334-bp gene GLGLS2 encoding membrane bound β-1,3-glucan synthases GLGLS1p and GLGLS2p with the predicted Mws of 199.64 kDa and 203.82 kDa from G. lucidum mycelia, respectively. GLGLS2p was further partially purified and identified from cultivated mycelia of G. lucidum as the potential key β-1, 3-glucan synthase for the β-glucan biosynthesis. GLGLS2p showed high specificity to UDP-glucose with a K_m value of 79.54 µM and synthesize β-1, 3-glucan with a maximum degree of polymerization (DP) of 54. The AlphaFold 2 and molecular docking indicated that substrate UDP-glucose bound to seven amino acid residues of GLGLS2p via hydrogen bonds. These findings would provide insights into the knowledge of the glucan synthesis and catalytic mechanism of β-1,3-glucan synthases in G. lucidum.