The AddAB helicase–nuclease catalyses rapid and processive DNA unwinding using a single Superfamily 1A motor domain

• Published in: Nucleic acids research Vol. 39; no. 6; pp. 2271 - 2285
• Main Authors: Yeeles, Joseph T.P., Gwynn, Emma J., Webb, Martin R., Dillingham, Mark S.
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.03.2011
• Subjects: Amino Acid Motifs; Bacillus subtilis; binding sites; Biocatalysis; crystal structure; Dimerization; DNA - metabolism; DNA damage; DNA helicases; DNA Helicases - chemistry; DNA Helicases - genetics; DNA Helicases - metabolism; DNA, Single-Stranded - metabolism; Exodeoxyribonucleases - chemistry; Exodeoxyribonucleases - genetics; Exodeoxyribonucleases - metabolism; Mutation; Nucleic Acid Enzymes; Protein Structure, Tertiary; Protein Subunits - metabolism; single-stranded DNA
• ISSN: 0305-1048; 1362-4962; 1362-4962
• DOI: 10.1093/nar/gkq1124

The oligomeric state of Superfamily I DNA helicases is the subject of considerable and ongoing debate. While models based on crystal structures imply that a single helicase core domain is sufficient for DNA unwinding activity, biochemical data from several related enzymes suggest that a higher order oligomeric species is required. In this work we characterize the helicase activity of the AddAB helicase-nuclease, which is involved in the repair of double-stranded DNA breaks in Bacillus subtilis. We show that the enzyme is functional as a heterodimer of the AddA and AddB subunits, that it is a rapid and processive DNA helicase, and that it catalyses DNA unwinding using one single-stranded DNA motor of 3' → 5' polarity located in the AddA subunit. The AddB subunit contains a second putative ATP-binding pocket, but this does not contribute to the observed helicase activity and may instead be involved in the recognition of recombination hotspot sequences.