TreT, a novel trehalose glycosyltransferring synthase of the hyperthermophilic Archaeon Thermococcus litoralis

The gene cluster in Thermococcus litoralis encoding a multicomponent and binding protein-dependent ABC transporter for trehalose and maltose contains an open reading frame of unknown function. We cloned this gene (now called treT), expressed it in Escherichia coli, purified the encoded protein, and identified it as an enzyme forming trehalose and ADP from ADP-glucose and glucose. The enzyme can also use UDP- and GDP-glucose but with less efficiency. The reaction is reversible, and ADP-glucose plus glucose can also be formed from trehalose and ADP. The rate of reaction and the equilibrium favor the formation of trehalose. At 90degreesC, the optimal temperature for the enzymatic reaction, the half-maximal concentration of ADP-glucose at saturating glucose concentrations is 1.14 mM and the V-max is 160 units/mg protein. In the reverse reaction, the half-maximal concentration of trehalose at saturating ADP concentrations is 11.5 mM and the V-max was estimated to be 17 units/mg protein. Under non-denaturating in vitro conditions the enzyme behaves as a dimer of identical subunits of 48 kDa. As the transporter encoded in the same gene cluster, TreT is induced by trehalose and maltose in the growth medium.