Lpg0406, a hypothetical protein from Legionella pneumophila, belongs to carboxymuconolactone decarboxylase (CMD) family. We determined the crystal structure of lpg0406 both in its apo and reduced form. The structures reveal that lpg0406 forms a hexamer and have disulfide exchange properties. The protein has an all-helical fold with a conserved thioredoxin-like active site CXXC motif and a proton relay system similar to that of alkylhydroperoxidase from Mycobacterium tuberculosis (MtAhpD), suggesting that lpg0406 might function as an enzyme with peroxidase activity and involved in antioxidant defense. A comparison of the size and the surface topology of the putative substrate-binding region between lpg0406 and MtAhpD indicates that the two enzymes accommodate the different substrate preferences. The structural findings will enhance understanding of the CMD family protein structure and its various functions.

AmyP is a raw-starch-degrading -amylase newly identified from a marine metagenome library. It shares low sequence similarity with characterized glycoside hydrolases and was classified into a new subfamily of GH13. In particular, it showed preferential degradation to raw rice starch. Full-length AmyP was cloned and overexpressed in Escherichia coli, then purified and crystallized in the presence of its substrate analogue -cyclodextrin. X-ray diffraction data were collected to a resolution of 2.1 Å . The crystal belonged to space group P2 1 2 1 2, with unit-cell parameters a = 129.824, b = 215.534, c = 79.699 Å , = = = 90, and was estimated to contain two molecules in one asymmetric unit.