One-step purification and immobilization of thermophilic polyphosphate glucokinase from Thermobifida fusca YX: glucose-6-phosphate generation without ATP.

The discovery of stable and active polyphosphate glucokinase (PPGK, EC 2.7.1.63) would be vital to cascade enzyme biocatalysis that does not require a costly ATP input. An open reading frame Tfu_1811 from Thermobifida fusca YX encoding a putative PPGK was cloned and the recombinant protein fused with a family 3 cellulose-binding module (CBM-PPGK) was overexpressed in Escherichia coli. Mg²⁺ was an indispensible activator. This enzyme exhibited the highest activity in the presence of 4 mM Mg²⁺ at 55°C and pH 9.0. Under its suboptimal conditions (pH 7.5), the k (cat) and K(m) values of CBM-PPGK on glucose were 96.9 and 39.7 s⁻¹ as well as 0.77 and 0.45 mM at 37°C and 50°C respectively. The thermoinactivation of CBM-PPGK was independent of its mass concentration. Through one-step enzyme purification and immobilization on a high-capacity regenerated amorphous cellulose, immobilized CBM-PPGK had an approximately eightfold half lifetime enhancement (i.e., t(1/2) = 120 min) as compared to free enzyme at 50°C. To our limited knowledge, this enzyme was the first thermostable PPGK reported. Free PPGK and immobilized CBM-PPGK had total turnover number values of 126,000 and 961,000 mol product per mol enzyme, respectively, suggesting their great potential in glucose-6-phosphate generation based on low-cost polyphosphate.