Characterization of a glucan phosphorylase from the thermophilic archaeon Sulfolobus tokodaii strain 7

A glucan phosphorylase from the hyperthermoacidophilic crenarchaeaon Sulfolobus tokodaii strain 7 (stGP) was characterized. The enzyme displayed maximum activity at 75 °C and pH 6.0 and was highly stable at 95 °C. The enzyme showed distinct substrate specificity, with maltose being the minimum primer for glucan synthesis and maltotriose being the minimum substrate for degradation. Interestingly, the sequences of GPs from Crenarchaeota clustered all together and formed a distinct lineage. Compared with previously characterized GPs, stGP (56 kDa) was much smaller. Structure modeling revealed that stGP was more compact than other GPs and it seemed that stGP was more primitive and adaptable to high temperature. Taken together, stGP and its homologues in Crenarchaeota probably constitute a novel group of GPs.