The Structure of the Biofilm-controlling Response Regulator BfmR from Acinetobacter baumannii Reveals Details of Its DNA-binding Mechanism

Abstract

The rise of drug-resistant bacterial infections coupled with decreasing antibiotic efficacy poses a significant challenge to global health care. Acinetobacter baumannii is an insidious, emerging bacterial pathogen responsible for severe nosocomial infections aided by its ability to form biofilms. The response regulator BfmR, from the BfmR/S two-component system, is the master regulator of biofilm initiation in A. baumannii and is a tractable therapeutic target. Here we present the structure of A. baumannii BfmR using a hybrid approach combining X-ray crystallography, nuclear magnetic resonance spectroscopy, chemical crosslinking mass spectrometry, and molecular modeling. We also show that BfmR binds the previously proposed bfmRS promoter sequence with moderate affinity. While BfmR shares many traits with other OmpR/PhoB family response regulators, some unusual properties were observed. Most importantly, we observe that when phosphorylated, BfmR binds this promoter sequence with a lower affinity than when not phosphorylated. All other OmpR/PhoB family members studied to date show an increase in DNA-binding affinity upon phosphorylation. Understanding the structural and biochemical mechanisms of BfmR will aid in the development of new antimicrobial therapies.

Francisella novicida Two-Component System Response Regulator BfpR Modulates iglC Gene Expression, Antimicrobial Peptide Resistance, and Biofilm Production

“…On average, the Cα backbone align with an average RMSD of about 0.9 Å across ∼110 atoms (Figure 3). The asymmetric unit of BfpR contains one monomer with an adjacent symmetry mate forming the biologically relevant dimer ( Figure 2B) as described previously (Milton et al, 2017;Draughn et al, 2018). The dimer α4-β5-α5 interface of BfpR contains major salt bridges between Lys92 and Glu112, Asp102 and Arg116, and Asp101 and Arg123.…”

“…Using a 2-aminoimidazole-based compound that targets response regulators, we have previously shown that we can inhibit BfmR, a master controller of biofilm in Acinetobacter baumannii (Thompson et al, 2012;Milton et al, 2017), and F. novicida QseB (Milton et al, 2017;Draughn et al, 2018). These results suggest that response regulators are a potential therapeutic target.…”

“…A calcium ion is coordinated into the position of the active site magnesium (Figure 2C). It has been previously demonstrated that the crystal lattice appears to trap the response regulator in an active state, even in the absence of phosphate or a phosphomimic (Draughn et al, 2018). This was demonstrated with the response regulator BfmR, the master biofilm regulator from Acinetobacter baumannii.…”

“…The dimer α4-β5-α5 interface of BfpR contains major salt bridges between Lys92 and Glu112, Asp102 and Arg116, and Asp101 and Arg123. These residues have been shown to have homology in other OmpR/PhoP family response regulators (Draughn et al, 2018). The BfpR active site contains the canonical conserved aspartate residues, including the phosphorylation site at Asp55.…”

Structural insights into the histidine-containing phosphotransfer protein and receiver domain of sensor histidine kinase suggest a complex model in the two-component regulatory system inPseudomonas aeruginosa

“…Although the loops and some residues may undergo conformational changes during phosphorylation, there is no dramatic structural rearrangement in the main secondarystructure architecture of receiver domains (Lee et al, 2001). For example, the difference is small between the structures of BeF 3 À BfmRN and the apo form BfmRN, with an RMSD of 0.315 across 227 C atoms (Draughn et al, 2018). The structural differences between PA1611REC in the apo form and the complex model are also small, with an RMSD of 0.43 Å .…”