4cei
From Proteopedia
Crystal structure of ADPNP-bound AddAB with a forked DNA substrate
Structural highlights
FunctionADDA_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] 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 (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 chi 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 chi 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 chi-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 chi sequences, and explains how chi recognition leads to the arrest of AddAB (and RecBCD) translocation that is observed in single-molecule experiments. Structural basis for translocation by AddAB helicase-nuclease and its arrest at chi sites.,Krajewski WW, Fu X, Wilkinson M, Cronin NB, Dillingham MS, Wigley DB Nature. 2014 Mar 16. doi: 10.1038/nature13037. PMID:24670664[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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