3u4q
From Proteopedia
Structure of AddAB-DNA complex at 2.8 angstroms
Structural highlights
Function[ADDA_BACSU] An essential component of the DNA double-stranded break repair machinery, the heterodimer acts as both an ATP-dependent DNA helicase and an ATP-dependent, dual-direction single-stranded exonuclease. Recognizes the B.subtilis chi site (5'-AGCGG-3') which transforms the enzyme from a helicase which degrades both DNA strands to one with only 5' -> 3' exonuclease activity. This generates a double-stranded DNA with a protruding 3'-terminated single-stranded tail suitable for the initiation of homologous recombination (chi fragment). The AddA nuclease domain in particular is required for chi fragment generation; this subunit has 3' -> 5' nuclease and helicase activity. RecA thread formation during DNA double-strand break repair requires RecJ or AddAB.[1] [2] [3] [ADDB_BACSU] The heterodimer acts as both an ATP-dependent DNA helicase and an ATP-dependent single-stranded exonuclease, acting in both directions. Recognizes the B.subtilis chi site (5'-AGCGG-3') which transforms the enzyme from a helicase which degrades both DNA strands to one with only 5' to 3' exonuclease activity. This generates a double-stranded DNA with a protruding 3'-terminated single-stranded tail suitable for the initiation of homologous recombination (chi fragment). The AddB nuclease domain is not required for chi fragment generation; this subunit has 5' -> 3' nuclease activity. RecA thread formation during DNA double-strand break repair requires RecJ or AddAB.[4] [5] [6] Publication Abstract from PubMedIn bacterial cells, processing of double-stranded DNA breaks for repair by homologous recombination is dependent upon the recombination hotspot sequence Chi and is catalysed by either an AddAB- or RecBCD-type helicase-nuclease. Here, we report the crystal structure of AddAB bound to DNA. The structure allows identification of a putative Chi-recognition site in an inactivated helicase domain of the AddB subunit. By generating mutant protein complexes that do not respond to Chi, we show that residues responsible for Chi recognition are located in positions equivalent to the signature motifs of a conventional helicase. Comparison with the related RecBCD complex, which recognizes a different Chi sequence, provides further insight into the structural basis for sequence-specific ssDNA recognition. The structure suggests a simple mechanism for DNA break processing, explains how AddAB and RecBCD can accomplish the same overall reaction with different sets of functional modules and reveals details of the role of an Fe-S cluster in protein stability and DNA binding. Insights into Chi recognition from the structure of an AddAB-type helicase-nuclease complex.,Saikrishnan K, Yeeles JT, Gilhooly NS, Krajewski WW, Dillingham MS, Wigley DB EMBO J. 2012 Feb 3. doi: 10.1038/emboj.2012.9. PMID:22307084[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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