Towards the three-dimensional structure of a sucrose isomerase from Pseudomonas mesoacidophila MX-45

Abstract: The trehalulose synthase MutB from Pseudomonas mesoacidophilaMX-45 is a member of the glycoside hydrolase family 13, although its biological function is the isomerization of sucrose to produce trehalulose and isomaltulose, with a yield of 90 % of trehalulose at 20◦C and pH 5.5-6.5. Here we report and compare the structures of two crystal forms of MutB, solved to 1.8 A ̊ and 1.6 A ̊ resolution, respectively. This is the first reported structure of a trehalulose synthase and the second structure of a sucrose isomerase, the first one being that of the isomaltulose synthase PalI from Klebsiella sp. LX3. Despite important biochemical and enzymatic differences, both enzymes display quite high sequence identity and share a common fold composed of three domains: the N-terminal catalytic domain containing a modified (β/α)8-barrel, a subdomain and the C-terminal domain. A detailed structural comparison appears to be an essential approach for the understanding of differences in enzymatic properties, including product specificity