title: Quasi-equivalence in site-specific recombinase structure and function: crystal structure and activity of trimeric Cre recombinase bound to a three-way Lox DNA junction.
abstract: The crystal structure of a novel Cre-Lox synapse was solved using phases from multiple isomorphous replacement and anomalous scattering, and refined to 2.05 A resolution. In this complex, a symmetric protein trimer is bound to a Y-shaped three-way DNA junction, a marked departure from the pseudo-4-fold symmetrical tetramer associated with Cre-mediated LoxP recombination. The three-way DNA junction was accommodated by a simple kink without significant distortion of the adjoining DNA duplexes. Although the mean angle between DNA arms in the Y and X structures was similar, adjacent Cre trimer subunits rotated 29 degrees relative to those in the tetramers. This rotation was accommodated at the protein-protein and DNA-DNA interfaces by interactions that are "quasi-equivalent" to those in the tetramer, analogous to packing differences of chemically identical viral subunits at non-equivalent positions in icosahedral capsids. This structural quasi-equivalence extends to function as Cre can bind to, cleave and perform strand transfer with a three-way Lox substrate. The structure explains the dual recognition of three and four-way junctions by site-specific recombinases as being due to shared structural features between the differently branched substrates and plasticity of the protein-protein interfaces. To our knowledge, this is the first direct demonstration of quasi-equivalence in both the assembly and function of an oligomeric enzyme.
authors.affiliation: Section of Molecular and Cellular Biology, University of California, Davis, 1 Shields Ave, Davis, CA 95616, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Woods
authors.forename: S S
authors.initials: SS
authors.lastname: Martin
authors.forename: V C
authors.initials: VC
authors.lastname: Chu
authors.forename: E P
authors.initials: EP
authors.lastname: Baldwin
mesh_terms: D001287:Attachment Sites, Microbiological / Q000235:genetics*; D001483:Base Sequence; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D004269:DNA, Bacterial / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D019426:Integrases / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D011995:Recombination, Genetic; D012399:Rotation; D013329:Structure-Activity Relationship; D014764:Viral Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D021122:Protein Subunits; D014764:Viral Proteins; C045073:Cre recombinase; D019426:Integrases