title: Loop-to-helix transition in the structure of multidrug regulator AcrR at the entrance of the drug-binding cavity.
abstract: Multidrug transcription regulator AcrR from Salmonella enterica subsp. enterica serovar Typhimurium str. LT2 belongs to the tetracycline repressor family, one of the largest groups of bacterial transcription factors. The crystal structure of dimeric AcrR was determined and refined to 1.56Å resolution. The tertiary and quaternary structures of AcrR are similar to those of its homologs. The multidrug binding site was identified based on structural alignment with homologous proteins and has a di(hydroxyethyl)ether molecule bound. Residues from helices α4 and α7 shape the entry into this binding site. The structure of AcrR reveals that the extended helical conformation of helix α4 is stabilized by the hydrogen bond between Glu67 (helix α4) and Gln130 (helix α7). Based on the structural comparison with the closest homolog structure, the Escherichia coli AcrR, we propose that this hydrogen bond is responsible for control of the loop-to-helix transition within helix α4. This local conformational switch of helix α4 may be a key step in accessing the multidrug binding site and securing ligands at the binding site. Solution small-molecule binding studies suggest that AcrR binds ligands with their core chemical structure resembling the tetracyclic ring of cholesterol.
authors.affiliation: European Molecular Biology Laboratory (EMBL), Grenoble Outstation, 71 avenue des Martyrs, F-38042 Grenoble, France; Unit of Virus-Host Cell Interactions (UVHCI), University of Grenoble Alpes, F-38042 Grenoble, France.
authors.forename: Babu A
authors.initials: BA
authors.lastname: Manjasetty
authors.affiliation: Biochemistry and Molecular Genetics, Feinberg School of Medicine, Northwestern University, 303 East Chicago Avenue, Chicago, IL 60611, United States; Center for Structural Genomics of Infectious Diseases (CSGID), 303 East Chicago Avenue, Chicago, IL 60626, United States. Electronic address: a-halavaty@northwestern.edu.
authors.forename: Andrei S
authors.initials: AS
authors.lastname: Halavaty
authors.affiliation: Center for Structural Genomics of Infectious Diseases (CSGID), 303 East Chicago Avenue, Chicago, IL 60626, United States; High Throughput Analysis Laboratory, Northwestern University, 2205 Tech Drive, Evanston, IL 60208, United States.
authors.forename: Chi-Hao
authors.initials: CH
authors.lastname: Luan
authors.affiliation: Center for Structural Genomics of Infectious Diseases (CSGID), 303 East Chicago Avenue, Chicago, IL 60626, United States; Computational Institute, The University of Chicago, 5735 South Ellis Avenue, Chicago, IL 60637, United States; Structural Biology Center, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, United States.
authors.forename: Jerzy
authors.initials: J
authors.lastname: Osipiuk
authors.affiliation: Center for Structural Genomics of Infectious Diseases (CSGID), 303 East Chicago Avenue, Chicago, IL 60626, United States; Computational Institute, The University of Chicago, 5735 South Ellis Avenue, Chicago, IL 60637, United States; Structural Biology Center, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, United States.
authors.forename: Rory
authors.initials: R
authors.lastname: Mulligan
authors.affiliation: Center for Structural Genomics of Infectious Diseases (CSGID), 303 East Chicago Avenue, Chicago, IL 60626, United States; Infectious Diseases, J. Craig Venter Institute, 9714 Medical Center Dr. Rockville, MD 20850, United States.
authors.forename: Keehwan
authors.initials: K
authors.lastname: Kwon
authors.affiliation: Biochemistry and Molecular Genetics, Feinberg School of Medicine, Northwestern University, 303 East Chicago Avenue, Chicago, IL 60611, United States; Center for Structural Genomics of Infectious Diseases (CSGID), 303 East Chicago Avenue, Chicago, IL 60626, United States.
authors.forename: Wayne F
authors.initials: WF
authors.lastname: Anderson
authors.affiliation: Center for Structural Genomics of Infectious Diseases (CSGID), 303 East Chicago Avenue, Chicago, IL 60626, United States; Computational Institute, The University of Chicago, 5735 South Ellis Avenue, Chicago, IL 60637, United States; Structural Biology Center, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, United States. Electronic address: andrzejj@anl.gov.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Joachimiak
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008024:Ligands; D008958:Models, Molecular; D011485:Protein Binding; D000072417:Protein Domains; D017433:Protein Structure, Secondary; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid
chemical_list: D001426:Bacterial Proteins; D008024:Ligands; D012097:Repressor Proteins
keywords: Loop-to-helix transition; Multidrug resistance; TetR/AcrR; Transcription regulator