The structures of isomaltase fromSaccharomyces cerevisiaeand in complex with maltose were determined at resolutions of and A˚ , respec-tively. Isomaltase contains three domains, namely, A, B, and C. Domain A consists of the (b⁄a)8 -barrel common to glycoside hydrolase family 13. However, the folding of domain C is rarely seen in other glycoside hydro-lase family 13 enzymes.