Molecular investigation of a novel thermostable glucan phosphorylase from Thermoanaerobacter tengcongensis

The glgP gene in Thermoanaerobacter tengcongensis encodes a putative α-glucan phosphorylase (Tte-GlgP), which is much smaller than its homologs in most other bacteria and is grouped into a less-recognized family. To characterize this novel enzyme, it was overexpressed in Escherichia coli and purified to apparent homogeneity. This purified Tte-GlgP, with expected molecular size (∼64 kDa) and isoelectric point (∼pI 6.2), exhibited a wide substrate spectrum in transformation of a variety of glucans such as soluble starch, maltodextrins and glycogen into glucose-1-phosphate. Western blot analysis indicated that the production of Tte-GlgP in T. tengcongensis was repressed by glucose but induced by maltose slightly, suggesting that it was involved in the carbohydrate metabolism in this thermophile. The Tte-GlgP was optimally active at 60 °C, and was thermostable with 90% residual activity after treating at 60 °C for 6 h, thus the overexpressed Tte-GlgP might also be a good candidate for structure–function analysis in its family.