title: A model for dsDNA translocation revealed by a structural motif common to RecG and Mfd proteins.
abstract: RecG protein differs from other helicases analysed to atomic resolution in that it mediates strand separation via translocation on double-stranded (ds) rather than single-stranded (ss) DNA. We describe a highly conserved helical hairpin motif in RecG and show it to be important for helicase activity. It places two arginines (R609 and R630) in opposing positions within the component helices where they are stabilized by a network of hydrogen bonds involving a glutamate from helicase motif VI. We suggest that disruption of this feature, triggered by ATP hydrolysis, moves an adjacent loop structure in the dsDNA-binding channel and that a swinging arm motion of this loop drives translocation. Substitutions that reverse the charge at R609 or R630 reduce DNA unwinding and ATPase activities, and increase dsDNA binding, but do not affect branched DNA binding. Sequences forming the helical hairpin and loop structures are highly conserved in Mfd protein, a transcription-coupled DNA repair factor that also translocates on dsDNA. The possibility of type I restriction enzymes and chromatin-remodelling factors using similar structures to drive translocation on dsDNA is discussed.
authors.affiliation: Institute of Genetics, University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, UK.
authors.forename: Akeel A
authors.initials: AA
authors.lastname: Mahdi
authors.forename: Geoffrey S
authors.initials: GS
authors.lastname: Briggs
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Sharples
authors.forename: Qin
authors.initials: Q
authors.lastname: Wen
authors.forename: Robert G
authors.initials: RG
authors.lastname: Lloyd
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001120:Arginine / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D004247:DNA / Q000378:metabolism*; D004265:DNA Helicases / Q000737:chemistry* / Q000378:metabolism; D004261:DNA Replication / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D014157:Transcription Factors; C072103:transcription repair coupling factor protein, Bacteria; C071446:RecG protein, E coli; D000255:Adenosine Triphosphate; D004247:DNA; D001120:Arginine; D004265:DNA Helicases