A model for dsDNA translocation revealed by a structural motif common to RecG and Mfd proteins

• Published in: The EMBO journal 2003-02, Vol.22 (3), p.724-734
• Main Authors: Mahdi, Akeel A., Briggs, Geoffrey S., Sharples, Gary J., Wen, Qin, Lloyd, Robert G.
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Amino Acid Sequence; Arginine - metabolism; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Deoxyribonucleic acid; DNA; DNA - metabolism; DNA Helicases - chemistry; DNA Helicases - metabolism; DNA replication; DNA Replication - physiology; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; EMBO09; EMBO13; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - genetics; Escherichia coli Proteins - metabolism; Holliday junctions; Hydrogen Bonding; Models, Molecular; Molecular Sequence Data; Mutagenesis, Site-Directed; Protein Structure, Secondary; Protein Structure, Tertiary; RecB; recombination; repair; RuvABC; Sequence Alignment; Transcription Factors - chemistry; Transcription Factors - metabolism; Translocation
• ISSN: 0261-4189; 1460-2075; 1460-2075
• DOI: 10.1093/emboj/cdg043

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.