The subatomic resolution study of laccase inhibition by chloride and fluoride anions using single-Crystal serial crystallography: insights into the enzymatic reaction mechanism.
Laccases are enzymes that catalyze the oxidation of a wide range of organic and
inorganic substrates accompanied by the reduction of molecular oxygen to water.
Here, a subatomic resolution X-ray crystallographic study of the mechanism of
inhibition of the laccase from the basidiomycete fungus Steccherinum
murashkinskyi by chloride and fluoride ions is presented. Three series of X-ray
diffraction data sets were collected with increasing doses of absorbed X-ray
radiation from a native S. murashkinskyi laccase crystal and from crystals of
complexes of the laccase with chloride and fluoride ions. The data for the
native laccase crystal confirmed the previously deduced enzymatic mechanism of
molecular oxygen reduction. The structures of the complexes allowed the
localization of chloride and fluoride ions in the channel near the T2 copper
ion. These ions replace the oxygen ligand of the T2 copper ion in this channel
and can play the role of this ligand in the enzymatic reaction. As follows from
analysis of the structures from the increasing dose series, the inhibition of
laccases by chloride and fluoride anions can be explained by the fact that the
binding of these negatively charged ions at the position of the oxygen ligand of
the T2 copper ion impedes the reduction of the T2 copper ion.
