Unique metal dependency of cytosolic α-mannosidase from Thermotoga maritima, a hyperthermophilic bacterium

A putative cytosolic α-mannosidase gene from a hyperthermophilic marine bacterium Thermotoga maritima was cloned and expressed in Escherichia coli. The purified recombinant enzyme appeared to be a homodimer of a 110-kDa subunit. The enzyme showed metal-dependent ability to hydrolyze p-nitrophenyl-α-d-mannopyranoside. In the absence of a metal, the enzyme was inactive. Cobalt and cadmium supported high activity (60 U/mg at 70 °C), while the activity with zinc and chromium was poor. Cobalt (0.8 mol) bound to 1 mol monomer with a Kd of 70 μM. The optimum pH and temperature were 6.0 and 80 °C, respectively. The activity was inhibited by swainsonine, but not by 1-deoxymannojirimycin, which is in agreement with the features of cytosolic α-mannosidase.