4-α-Glucanotransferase from the hyperthermophilic archaeon <em>thermococcus litoralis</em>.

4-α-Glucanotransferase was purified from cells of Thermococcus litoralis, a hyperthermophilic archaeon. The molecular mass of the enzyme was estimated to be approximately 87 kDa by gel filtration. The optimal temperature for its activity was 90&#176;C. The enzyme catalyzed the transglycosylation of maltooligosaccharides, yielding maltooligosaccharides of various lengths and glucose. When maltoheptaose was used as the substrate, glucoamylase-resistant and glucoamylase-sensitive saccharides were produced. On incubation of amylose with the T. litoralis enzyme, glucoamylase-resistant but α-amylase—sensitive molecules were produced, but the amount of reducing sugar showed only slight increases. These results indicate that the T. litoralis enzyme catalyzes not only intermolecular transglycosylation to produce linear α-l,4-glucan, but also intramolecular transglycosylation to produce cyclic α-l,4-glucan (cycloamylose), similarly to potato 4-α-glucanotransferase (called disproportionating enzyme). The gene encoding the Z litoralis 4-α-glucanotransferase was cloned, sequenced and expressed in Escherichia coli. The nucleotide sequence of the gene encoded a 659-amino acid protein with a calculated molecular mass of 77 883 Da. The amino acid sequence of the T. titoralis enzyme showed high similarity with those of α-amylases of Pyrococcus furiosus, a hyperthermophilic archaeon, and Dictyoglomus thermophilum, an extremely thermophilic bacterium, but little similarity with those of other known 4-α-glucanotransferases. [ABSTRACT FROM AUTHOR]