title: Comprehensive characterization of ligand-induced plasticity changes in a dimeric enzyme.
abstract: An enzyme's inherent structural plasticity is frequently associated with substrate binding, yet detailed structural characterization of flexible proteins remains challenging. This study employs complementary biophysical methods to characterize the partially unfolded structure of substrate-free AAC(6')-Ii, an N-acetyltransferase of the GCN5-related N-acetyltransferase (GNAT) superfamily implicated in conferring broad-spectrum aminoglycoside resistance on Enterococcus faecium. The X-ray crystal structure of AAC(6')-Ii is analyzed to identify relative motions of the structural elements that constitute the dimeric enzyme. Comparison with the previously elucidated crystal structure of AAC(6')-Ii with acetyl coenzyme A (AcCoA) reveals conformational changes that occur upon substrate binding. Our understanding of the enzyme's structural plasticity is further refined with small-angle X-ray scattering and circular dichroism analyses, which together reveal how flexible structural elements impact dimerization and substrate binding. These results clarify the extent of unfolding that AAC(6')-Ii undergoes in the absence of AcCoA and provide a structural connection to previously observed allosteric cooperativity of this enzyme.
  
  
  
  Structural data are available in the PDB database under the accession number 5E96.
authors.affiliation: Department of Biochemistry, Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, QC, Canada.
authors.forename: Oliver M
authors.initials: OM
authors.lastname: Baettig
authors.affiliation: Department of Biochemistry, Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, QC, Canada.
authors.forename: Kun
authors.initials: K
authors.lastname: Shi
authors.affiliation: Department of Chemistry & Chemical Biology, Center for Integrative Proteomics, Rutgers University, Piscataway, NJ, USA.
authors.forename: Brahm J
authors.initials: BJ
authors.lastname: Yachnin
authors.affiliation: Department of Biochemistry, Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, QC, Canada.
authors.forename: David L
authors.initials: DL
authors.lastname: Burk
authors.affiliation: Department of Biochemistry, Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, QC, Canada.|Department of Microbiology and Immunology, Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, QC, Canada.
authors.forename: Albert M
authors.initials: AM
authors.lastname: Berghuis
mesh_terms: D000105:Acetyl Coenzyme A / Q000737:chemistry; D000123:Acetyltransferases / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry*; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D016984:Enterococcus faecium / Q000201:enzymology; D008024:Ligands; D008958:Models, Molecular; D011487:Protein Conformation; D055503:Protein Multimerization; D053838:Scattering, Small Angle; D014961:X-Ray Diffraction
chemical_list: D001426:Bacterial Proteins; D008024:Ligands; D000105:Acetyl Coenzyme A; D000123:Acetyltransferases
keywords: allosteric cooperativity; aminoglycoside 6′-N-acetyltransferase type-Ii; antibiotic resistance; ligand-induced plasticity; protein flexibility