Crystal structure of the flavin reductase of Acinetobacter baumannii p-hydroxyphenylacetate 3-hydroxylase (HPAH) and identification of amino acid residues underlying its regulation by aromatic ligands

Monooxygenation of aromatic compounds by flavin‐dependent monooxygenases

“…Recently, the structure of C 1 has been reported. 74 C 2 catalyzes the hydroxylation of HPA using oxygen and FMNH − , FADH − or reduced riboflavin as co-substrates. 54,70 For two-component flavin-dependent monooxygenases, the reduced flavin generated by a reductase has to be transferred to a corresponding monooxygenase.…”

“…15,76 In HPAH, the substrate HPA acts as an effector to stimulate the reduction of FMN by changing the enzyme into a more active conformation. 56,74,76 The rate constant of the FMN reduction increases by about 30 times in the presence of HPA. Recently, the X-ray structure of C 1 has been reported.…”

Creating Flavin Reductase Variants with Thermostable and Solvent‐Tolerant Properties by Rational‐Design Engineering

“…Furthermore, the results indicated that the binding of HPA to each C 1 variant can enhance thermotolerance. This could be explained in terms of the influence of a substantial conformational change in the C 1 variant upon HPA binding at the C‐terminal domain . Similarly enhanced structural stabilization upon ligand binding has also been observed in the cases of many other enzymes .…”

“…C 1 is unique among the flavin reductases in that the HPA substrate can stimulate the rates both of FMN reduction and of FMNH − release . X‐ray structures of FMN‐bound C 1 have been solved at 2.2 Å (PDB ID: 5ZYR; Oonanant et al., unpublished results) and 2.9 Å (PDB ID: 5ZC2) . The structural analyses indicated that C 1 exists as a homodimer and that each subunit consists of two domains: N‐ and C‐terminal domains (Figure S1).…”

“…The N‐terminal domain (residues 1–169) is a flavin reductase domain that contains tightly bound FMN, whereas the C‐terminal domain (residues 190–315) is predicted to be a MarR domain, typically found as a transcription factor. These two domains are linked by a flexible loop (residues 170–189) . Thanks to its redox reaction generating FMNH − , C 1 has been applied in the enzymatic cascade reactions of the bacterial luciferase (luxAB) from Vibrio campbellii and monooxygenase (C 2 ) to produce a bioluminescence signal as a promising eukaryote gene reporter or to synthesize trihydroxyphenolic acids such as 3,4,5‐trihydroxycinnamic acid (3,4,5‐THCA) and (3,4,5‐trihydroxyphenyl)acetic acid (3,4,5‐THPA), which are strong antioxidants.…”