Crystal Structure of the Transcriptional Regulator AcrR from Escherichia coli

Abstract

The AcrAB multidrug efflux pump, which belongs to the resistance nodulation division (RND) family, recognizes and extrudes a wide range of antibiotics and chemotherapeutic agents and causes the intrinsic antibiotic resistance in Escherichia coli. The expression of AcrAB is controlled by the transcriptional regulator AcrR, whose open reading frame is located 141 bp upstream of the acrAB operon. To understand the structural basis of AcrR regulation, we have determined the crystal structure of AcrR to 2.55-A resolution, revealing a dimeric two-domain molecule with an entirely helical architecture similar to members of the TetR family of transcriptional regulators. Each monomer of AcrR forms a multientrance pocket of 350 A(3) in the ligand-binding domain. The ligand-binding pocket is surrounded with mostly hydrophobic residues. In addition, a completely buried negatively charged glutamate, expected to be critical for drug binding, is located at the center of the binding pocket. The crystal structure provides novel insight into the mechanisms of ligand binding and AcrR regulation.

Epoxide-Mediated CifR Repression of cif Gene Expression Utilizes Two Binding Sites in Pseudomonas aeruginosa

“…The 35 nM affinity of CifR for the cifR proximal binding site is consistent with other TetR-family proteins, such as AcrR (20.2 nM) and CmeR (88 nM) in their affinity for their binding sites (23,35). The apparent dissociation constant for the morB proximal site is higher than that of the cifR proximal site, which may be attributable to differences in the sequences in these sites ( Fig.…”

Crystal structures of CmeR‐bile acid complexes from Campylobacter jejuni

“…8). Such a phenomenon has been previously observed with the crystal structure of QacR simultaneously bound to two ligands, proflavin and ethidium, 19 and has been predicted through biochemical analysis to occur in many other proteins, including AcrR, 22,23 TtgV 24 and MdfA. 25 It has also been reported that the QacR repressor can bind a single ligand in multiple positions, 26 possibly due to the multifaceted nature of this protein.…”

Crystal structure of the transcriptional regulator Rv1219c of Mycobacterium tuberculosis

“…16 This is evident through protein sequence alignment that residues 7-60 of Rv1219c possess 25%, 24%, and 31% amino acid identity to TetR, 17 QacR, 18 and Rv3066, 14 respectively. In addition, superimposition of the Ca atoms of this N-terminal region, between residues 7 and 60, with those of AcrR 19 and Rv3066 14 results in overall rms deviations of 3.1 and 3.2 Å .…”

“…The corresponding distances between the two recognition helices of the DNAbinding domains are 35,39, and 42 Å in the apo forms of TetR, 17 QacR, 18 and AcrR. 19 Given that the separation between two successive major grooves of a B-form DNA is 34 Å , the large center-to-center distance of Rv1219c may allow this regulator to span three consecutive major grooves of the promoter DNA.…”

“…The interlocking system may also allow the two N-terminal DNA-binding domains of the dimer to shift away from each other while still maintaining the dimeric form of the regulator. Although the C-terminal region displays no primary sequence conservation among members of the TetR family, the overall structure of the C-terminal domain of Rv1219c exhibits topological similarity to those of AcrR, 19 Rv3066, 14 EthR, 20,21 QacR, 18 and CmeR. 22 The crystal structure of Rv1219c also revealed that the C-terminal a-helical bundle of each subunit of the regulator forms a large internal cavity, with an internal volume of 802 Å 3 .…”