title: Crystal structure of the excisionase-DNA complex from bacteriophage lambda.
abstract: The excisionase (Xis) protein from bacteriophage lambda is the best characterized member of a large family of recombination directionality factors that control integrase-mediated DNA rearrangements. It triggers phage excision by cooperatively binding to sites X1 and X2 within the phage, bending DNA significantly and recruiting the phage-encoded integrase (Int) protein to site P2. We have determined the co-crystal structure of Xis with its X2 DNA-binding site at 1.7A resolution. Xis forms a unique winged-helix motif that interacts with the major and minor grooves of its binding site using an alpha-helix and an ordered beta-hairpin (wing), respectively. Recognition is achieved through an elaborate water-mediated hydrogen-bonding network at the major groove interface, while the preformed hairpin forms largely non-specific interactions with the minor groove. The structure of the complex provides insights into how Xis recruits Int cooperatively, and suggests a plausible mechanism by which it may distort longer DNA fragments significantly. It reveals a surface on the protein that is likely to mediate Xis-Xis interactions required for its cooperative binding to DNA.
authors.affiliation: Department of Chemistry and Biochemistry and the UCLA-DOE Institute for Genomics and Proteomics, University of California, Los Angeles, 405 Hilgard Ave., Los Angeles, CA 90095-1570, USA.
authors.forename: My D
authors.initials: MD
authors.lastname: Sam
authors.forename: Duilio
authors.initials: D
authors.lastname: Cascio
authors.forename: Reid C
authors.initials: RC
authors.lastname: Johnson
authors.forename: Robert T
authors.initials: RT
authors.lastname: Clubb
mesh_terms: D000595:Amino Acid Sequence; D010582:Bacteriophage lambda / Q000201:enzymology*; D001483:Base Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004254:DNA Nucleotidyltransferases / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009690:Nucleic Acid Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D014764:Viral Proteins
chemical_list: D014764:Viral Proteins; D004247:DNA; D004254:DNA Nucleotidyltransferases; C063911:excisionase