posted on 2022-01-06, 15:33authored byNarin Lawan, Ruchanok Tinikul, Panida Surawatanawong, Adrian J. Mulholland, Pimchai Chaiyen
Bacterial
luciferase (Lux) catalyzes oxidation of reduced flavin
mononucleotide (FMN) and aldehyde to form oxidized FMN and carboxylic
acid via molecular oxygen with concomitant light generation. The enzyme
is useful for various detection applications in biomedical experiments.
Upon reacting with oxygen, the reduced FMN generates C4a-peroxy-FMN
(FMNH-C4a–OO–) as a reactive intermediate,
which is required for light generation. However, the mechanism and
control of FMNH-C4a–OO– formation are not
clear. This work investigated the reaction of FMNH-C4a–OO– formation in Lux using QM/MM methods. The B3LYP/6-31G*/CHARMM27
calculations indicate that Lux controls the formation of FMNH-C4a–OO– via the conserved His44 residue. The steps in intermediate
formation are found to be as follows: (i) H+ reacts with
O2 to generate +OOH. (ii) +OOH attacks
C4a of FMNH– to generate FMNH-C4a–OOH. (iii)
H+ is transferred from FMNH-C4a–OOH to His44 to
generate FMNH-C4a–OO– while His44 stabilizes
FMNH-C4a–OO– by forming a hydrogen bond to
an oxygen atom. This controlling key mechanism for driving the change
from FMNH-C4a–OOH to the FMNH-C4a–OO– adduct is confirmed because FMNH-C4a–OO– is more stable than FMNH-C4a–OOH in the luciferase active
site.