Structure of an aryl esterase from Pseudomonas fluorescens

The structure of PFE, an aryl esterase from Pseudomonas fluorescens, has been solved to a resolution of 1.8 Å by X-ray diffraction and shows a characteristic α/β-hydrolase fold. In addition to catalyzing the hydrolysis of esters in vitro, PFE also shows low bromoperoxidase activity. PFE shows highest structural similarity, including the active-site environment, to a family of non-heme bacterial haloperoxidases, with an r.m.s. deviation in 271 C^α atoms between PFE and its five closest structural neighbors averaging 0.8 Å. PFE has far less similarity (r.m.s. deviation in 218 C^α atoms of 5.0 Å) to P. fluorescens carboxyl esterase. PFE favors activated esters with small acyl groups, such as phenyl acetate. The X-ray structure of PFE reveals a significantly occluded active site. In addition, several residues, including Trp28 and Met95, limit the size of the acyl-binding pocket, explaining its preference for small acyl groups.