title: Structural basis for translocation by AddAB helicase-nuclease and its arrest at χ sites.
abstract: In bacterial cells, processing of double-stranded DNA breaks for repair by homologous recombination is dependent upon the recombination hotspot sequence χ (Chi) and is catalysed by either an AddAB- or RecBCD-type helicase-nuclease (reviewed in refs 3, 4). These enzyme complexes unwind and digest the DNA duplex from the broken end until they encounter a χ sequence, whereupon they produce a 3' single-stranded DNA tail onto which they initiate loading of the RecA protein. Consequently, regulation of the AddAB/RecBCD complex by χ is a key control point in DNA repair and other processes involving genetic recombination. Here we report crystal structures of Bacillus subtilis AddAB in complex with different χ-containing DNA substrates either with or without a non-hydrolysable ATP analogue. Comparison of these structures suggests a mechanism for DNA translocation and unwinding, suggests how the enzyme binds specifically to χ sequences, and explains how χ recognition leads to the arrest of AddAB (and RecBCD) translocation that is observed in single-molecule experiments.
authors.affiliation: 1] Division of Structural Biology, Institute of Cancer Research, Chester Beatty Laboratories, 237 Fulham Road, London SW3 6JB, UK [2] CRT Discovery Laboratories, Department of Biological Sciences, Birkbeck, University of London, London WC1E 7HX, UK.
authors.forename: Wojciech W
authors.initials: WW
authors.lastname: Krajewski
authors.affiliation: Division of Structural Biology, Institute of Cancer Research, Chester Beatty Laboratories, 237 Fulham Road, London SW3 6JB, UK.
authors.forename: Xin
authors.initials: X
authors.lastname: Fu
authors.affiliation: Division of Structural Biology, Institute of Cancer Research, Chester Beatty Laboratories, 237 Fulham Road, London SW3 6JB, UK.
authors.forename: Martin
authors.initials: M
authors.lastname: Wilkinson
authors.affiliation: Division of Structural Biology, Institute of Cancer Research, Chester Beatty Laboratories, 237 Fulham Road, London SW3 6JB, UK.
authors.forename: Nora B
authors.initials: NB
authors.lastname: Cronin
authors.affiliation: School of Biochemistry, University of Bristol, Medical Sciences Building, University Walk, Bristol BS8 1TD, UK.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Dillingham
authors.affiliation: Division of Structural Biology, Institute of Cancer Research, Chester Beatty Laboratories, 237 Fulham Road, London SW3 6JB, UK.
authors.forename: Dale B
authors.initials: DB
authors.lastname: Wigley
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D001412:Bacillus subtilis / Q000201:enzymology*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004265:DNA Helicases / Q000737:chemistry* / Q000378:metabolism; D005090:Exodeoxyribonucleases / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008968:Molecular Conformation; D011995:Recombination, Genetic / Q000235:genetics*; D013329:Structure-Activity Relationship
chemical_list: D001426:Bacterial Proteins; D000255:Adenosine Triphosphate; D004247:DNA; D005090:Exodeoxyribonucleases; C080948:AddA protein, Bacillus subtilis; C080949:AddB protein, Bacillus subtilis; D004265:DNA Helicases