Unveiling the Pathways of Dioxygen Through the C2 Component of the Environmentally Relevant Monooxygenase p-Hydroxyphenylacetate Hydroxylase from Acinetobacter baumannii: A Molecular Dynamics Investigation.

Abstract

In this work, models of the homotetrameric C2 component of the monooxygenase p-hydroxyphenylacetate hydroxylase from Acinetobacter baumannii, in complex with dioxygen (O2 ) and, or not, the substrate p-hydroxyphenylacetate (HPA) were built. Both models proved to be amenable to random-acceleration molecular dynamics (RAMD) simulations, whereby a tiny randomly oriented external force, acting on O2 at the active site in front of flavin mononucleotide (FMNH(-) ), accelerated displacement of O2 toward the bulk solvent. This allowed us to carry out a sufficiently large number of RAMD simulations to be of statistical significance. The two systems behaved very similarly under RAMD, except for O2 leaving the active site more easily in the absence of HPA, but then finding similar obstacles in getting to the gate as when the active site was sheltered by HPA. This challenges previous conclusions that HPA can only reach the active center after that the C4aOOH derivative of FMNH(-) is formed, requiring uptake of O2 at the active site before HPA. According to these RAMD simulations, O2 could well get to FMNH(-) also in the presence of the substrate at the active site.