THA_1941 from Thermosipho africanus: A Thermostable β-1,3-Glucan Phosphorylase for Efficient β-1,3-Glucan Synthesis

{beta}-1,3-Glucan phosphorylases capable of utilizing glucose as a priming substrate are key biocatalysts for the synthesis of functional {beta}-1,3-glucan. In this study, we identified THA_1941 from Thermosipho africanus (Ta{beta}GP) as a GH161 {beta}-1,3-glucan phosphorylase exhibiting robust synthetic activity towards glucose, as confirmed by 13C nuclear magnetic resonance, liquid chromatography-mass spectrometry, and sequence and structural analyses. Ta{beta}GP displayed exceptional thermostability, retaining 93% of its activity at 60 {degrees}C for 180 h, and showed broad pH tolerance ranging from pH 5.0 to 10.0, surpassing the performance of previously reported homologs. In addition, Ta{beta}GP exhibited broad substrate flexibility, accepting both - and {beta}-linked disaccharides, and demonstrated strong resistance to metal ions and lignocellulose-derived inhibitors. In the presence of 150 mM glucose 1-phosphate as the donor substrate, Ta{beta}GP synthesized {beta}-1,3-glucan with a tunable average degree of polymerization (10-32), depending on the concentration of glucose used as the primer. The combination of thermostability, inhibitor resistance, and substrate versatility makes Ta{beta}GP a promising biocatalyst for the economically viable and environmentally sustainable synthesis of {beta}-1,3-glucan from non-food biomass sources.