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The Substrate-Bound Crystal Structure of a Baeyer–Villiger Monooxygenase Exhibits a Criegee-like Conformation
journal contribution
posted on 2015-12-16, 21:21 authored by Brahm
J. Yachnin, Tara Sprules, Michelle B. McEvoy, Peter C. K. Lau, Albert M. BerghuisThe Baeyer–Villiger monooxygenases (BVMOs) are
a family of bacterial flavoproteins that catalyze the synthetically
useful Baeyer–Villiger oxidation reaction. This involves the
conversion of ketones into esters or cyclic ketones into lactones
by introducing an oxygen atom adjacent to the carbonyl group. The
BVMOs offer exquisite regio- and enantiospecificity while acting on
a wide range of substrates. They use only NADPH and oxygen as cosubstrates,
and produce only NADP+ and water as byproducts, making
them environmentally attractive for industrial purposes. Here, we
report the first crystal structure of a BVMO, cyclohexanone monooxygenase
(CHMO) from Rhodococcus sp. HI-31 in complex with
its substrate, cyclohexanone, as well as NADP+ and FAD,
to 2.4 Å resolution. This structure shows a drastic rotation
of the NADP+ cofactor in comparison to previously reported
NADP+-bound structures, as the nicotinamide moiety is no
longer positioned above the flavin ring. Instead, the substrate, cyclohexanone,
is found at this location, in an appropriate position for the formation
of the Criegee intermediate. The rotation of NADP+ permits
the substrate to gain access to the reactive flavin peroxyanion intermediate
while preventing it from diffusing out of the active site. The structure
thus reveals the conformation of the enzyme during the key catalytic
step. CHMO is proposed to undergo a series of conformational changes
to gradually move the substrate from the solvent, via binding in a
solvent excluded pocket that dictates the enzyme’s chemospecificity,
to a location above the flavin–peroxide adduct where catalysis
occurs.