title: Solvent reorganization plays a temperature-dependent role in antibiotic selection by a thermostable aminoglycoside nucleotidyltransferase-4'.
abstract: The aminoglycoside nucleotidyltransferase-4' (ANT) is an enzyme that causes resistance to a large number of aminoglycoside antibiotics by nucleotidylation of the 4'-site on these antibiotics. The effect of solvent reorganization on enzyme-ligand interactions was investigated using a thermophilic variant of the enzyme resulting from a single-site mutation (T130K). Data showed that the binding of aminoglycosides to ANT causes exposure of polar groups to solvent. However, solvent reorganization becomes the major contributor to the enthalpy of the formation of enzyme-aminoglycoside complexes only above 20 °C. The change in heat capacity (ΔCp) shows an aminoglycoside-dependent pattern such that it correlates with the affinity of the ligand for the enzyme. Differences in ΔCp values determined in H2O and D2O also correlated with the ligand affinity. The temperature-dependent increase in the offset temperature (Toff), the temperature difference required to observe equal enthalpies in both solvents, is also dependent on the binding affinity of the ligand, and the steepest increase was observed with the tightest binding aminoglycoside, neomycin. Overall, these data, together with earlier observations with a different enzyme, the aminoglycoside N3-acetyltransferase-IIIb [Norris, A. L., and Serpersu, E. H. (2011) Biochemistry 50, 9309], show that solvent reorganization or changes in soft vibrational modes of the protein are interchangeable with respect to the role of being the major contributor to complex formation depending on temperature. These data suggest that such effects may more generally apply to enzyme-ligand interactions, and studies at a single temperature may provide only a part of the whole picture of thermodynamics of enzyme-ligand interactions.
authors.affiliation: Department of Biochemistry and Cellular and Molecular Biology, The University of Tennessee , Knoxville, Tennessee 37996, United States.
authors.forename: Xiaomin
authors.initials: X
authors.lastname: Jing
authors.forename: Engin H
authors.initials: EH
authors.lastname: Serpersu
mesh_terms: D000617:Aminoglycosides / Q000737:chemistry*; D000900:Anti-Bacterial Agents / Q000737:chemistry*; D002151:Calorimetry; D004795:Enzyme Stability; D006358:Hot Temperature; D009713:Nucleotidyltransferases / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D012997:Solvents; D009713:Nucleotidyltransferases