Crystal structure of diisopropylfluorophosphatase from Loligo vulgaris

Background: Phosphotriesterases (PTE) are enzymes capable of detoxifying or ganophosphate-based chemical warfare agents by hydrolysis. One subclass of these enzymes comprises the family of diisopropylfluorophosphatases (DFPase s). The DFPase reported here was originally isolated from squid head gangli on of Loligo vulgaris and can be characterized as squid-type DFPase. It is capable of hydrolyzing the organophosphates diisopropylfluorophosphate, som an, sarin, tabun, and cyclosarin. Results: Crystals were grown of both the native and the selenomethionine-la beled enzyme. The X-ray crystal structure of the DFPase from Loligo vulgari s has been solved by MAD phasing and refined to a crystallographic R value of 17.6% at a final resolution of 1.8 Angstrom. Using site-directed mutagen esis, we have structurally and functionally characterized essential residue s in the active site of the enzyme. Conclusions: The crystal structure of the DFPase from Loligo vulgaris is th e first example of a structural characterization of a squid-type DFPase and the second crystal structure of a PTE determined to date. Therefore, it ma y serve as a structural model for squid-type DFPases in general. The overal l structure of this protein represents a six-fold beta propeller with two c alcium ions bound in a central water-filled tunnel. The consensus motif fou nd in the blades of this beta propeller has not yet been observed in other beta propeller structures. Based on the results obtained from mutants of ac tive-site residues, a mechanistic model for the DFP hydrolysis has been dev eloped.