Refined Structure and Functional Implications of Trehalose Synthase from Sulfolobus acidocaldarius.

The three-dimensional structure of maltooligosyl trehalose synthase has been determined by the multiple isomorphous replacement method and refined at 1.9 Å resolution. The structure of the enzyme consists of three domains, A, B and C. The catalytic site resides between the C-terminal end of the central-barrel in the (β/α)8-structure of domains A and B, as in the usual α-amylase family enzymes. Domain C is composed of an eight-stranded β-sandwich structure. Domain A contains two large extra structural frameworks excursed from the barrel. These extra structures are shown to be indispensable to form the pocket at the active site where intramolecular transglycosylation takes place. A possible mechanism of catalysis is also discussed based on the refined structure.