X-ray diffraction structure of a cell-wall invertase from Arabidopsis thaliana

Cell-wall invertases play crucial roles during plant development. They hydrolyse sucrose into its fructose and glucose subunits by cleavage of the α1–β2 glycosidic bond. Here, the structure of the Arabidopsis thaliana cell-wall invertase 1 (AtcwINV1; gene accession code At3g13790) is described at a resolution of 2.15 Å. The structure comprises an N-terminal fivefold β-propeller domain followed by a C-terminal domain formed by two β-sheets. The active site is positioned in the fivefold β-propeller domain, containing the nucleophile Asp23 and the acid/base catalyst Glu203 of the double-displacement enzymatic reaction. The function of the C-terminal domain remains unknown. Unlike in other GH 32 family enzyme structures known to date, in AtcwINV1 the cleft formed between both domains is blocked by Asn299-linked carbohydrates. A preliminary site-directed mutagenesis experiment (Asn299Asp) removed the glycosyl chain but did not alter the activity profile of the enzyme.