title: The role of flexibility and hydration on the sequence-specific DNA recognition by the Tn916 integrase protein: a molecular dynamics analysis.
abstract: The N-terminal domain of the Tn916 integrase protein (INT-DBD) is responsible for DNA binding in the process of strand cleavage and joining reactions required for transposition of the Tn916 conjugative transposon. Site-specific association is facilitated by numerous protein-DNA contacts from the face of a three-stranded beta-sheet inserted into the major groove. The protein undergoes a subtle conformational transition and is slightly unfolded in the protein-DNA complex. The conformation of many charged residues is poorly defined by NMR data but mutational studies have indicated that removal of polar side chains decreases binding affinity, while non-polar contacts are malleable. Based on analysis of the binding enthalpy and binding heat capacity, we have reasoned that dehydration of the protein-DNA interface is incomplete. This study presents results from a molecular dynamics investigation of the INT-DBD-DNA complex aimed at a more detailed understanding of the role of conformational dynamics and hydration in site-specific binding. Comparison of simulations (total of 13 ns) of the free protein and of the bound protein conformation (in isolation or DNA-bound) reveals intrinsic flexibility in certain parts of the molecule. Conformational adaptation linked to partial unfolding appears to be induced by protein-DNA contacts. The protein-DNA hydrogen-bonding network is highly dynamic. The simulation identifies protein-DNA interactions that are poorly resolved or only surmised from the NMR ensemble. Single water molecules and water clusters dynamically optimize the complementarity of polar interactions at the 'wet' protein-DNA interface. The simulation results are useful to establish a qualitative link between experimental data on individual residue's contribution to binding affinity and thermodynamic properties of INT-DBD alone and in complex with DNA.
authors.affiliation: Biochemisches Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
authors.forename: Alemayehu A
authors.initials: AA
authors.lastname: Gorfe
authors.forename: Amedeo
authors.initials: A
authors.lastname: Caflisch
authors.forename: Ilian
authors.initials: I
authors.lastname: Jelesarov
mesh_terms: D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics; D019426:Integrases / Q000737:chemistry* / Q000235:genetics; D008968:Molecular Conformation; D019906:Nuclear Magnetic Resonance, Biomolecular; D018583:Pliability; D011487:Protein Conformation; D017510:Protein Folding; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D004268:DNA-Binding Proteins; D014867:Water; D019426:Integrases