Fluoroacetate dehalogenase
catalyzes the hydrolytic defluorination of
fluoroacetate to produce
glycolate. The
enzyme is unique in that it
catalyzes the cleavage of a
carbon-fluorine bond of an
aliphatic compound: the bond energy of the
carbon-fluorine bond is among the highest found in
natural products. The
enzyme also acts on
chloroacetate, although much less efficiently. We here determined the
X-ray crystal structure of the
enzyme from
Burkholderia sp. strain FA1 as the first experimentally determined three-dimensional structure of
fluoroacetate dehalogenase. The
enzyme belongs to the
alpha/beta hydrolase superfamily and exists as a homodimer. Each
subunit consists of core and cap domains. The
catalytic triad, Asp104-His271-Asp128, of which Asp104 serves as the
catalytic nucleophile, was found in the core domain at the domain interface. The
active site was composed of Phe34, Asp104, Arg105, Arg108, Asp128, His271, and Phe272 of the core domain and Tyr147, His149, Trp150, and Tyr212 of the cap domain. An
electron density peak corresponding to a
chloride ion was found in the vicinity of the N(epsilon1) atom of Trp150 and the N(epsilon2) atom of His149, suggesting that these are the
halide ion acceptors. Site-directed replacement of each of the active-site residues, except for Trp150, by
Ala caused the total loss of the activity toward
fluoroacetate and
chloroacetate, whereas the replacement of Trp150 caused the loss of the activity only toward
fluoroacetate. An interaction between Trp150 and the
fluorine atom is probably an absolute requirement for the reduction of the
activation energy for the cleavage of the
carbon-fluorine bond.
