Large‐scale structural rearrangement of a serine hydrolase from Francisella tularensis facilitates catalysis

Abstract

Amongst emerging targets for treating diverse bacterial infections are members of the ubiquitous serine hydrolase protein family. Herein, we present the crystal structure and biochemical characterization of FTT258, a novel bacterial carboxylesterase from F. tularensis and a homologue of human acyl protein thioesterase (hAPT1). The structure of FTT258 in the presence of a mechanistic cyclobutanone ligand reveals an unexpectedly large conformational change where the asymmetric unit for the FTT258 structure contains four open‐ and four closed‐forms of the protein. The large‐scale structural rearrangement in the open form is stabilized by the hydrophobic burial of a repositioned surface loop and is responsible for the exposure of the hydrophobic binding pocket. Residues within the newly exposed hydrophobic binding pocket and within the peripheral flexible loop proved essential to the hydrolytic activity of FTT258, indicating that structural rearrangement is required for catalytic activity. While the same residues in the flexible loop were not essential to membrane binding, FTT258 did show significant association with liposomes designed to mimic bacterial membranes. The observed conformational changes and connection to the catalytic activity suggest a potential dual regulation of catalytic activity and membrane association in FTT258. Funding provided by a Butler University Holcomb research award and NAIAD award HHSN272200700058C