National Center for
5FHF: Crystal Structure Of Bacteroides Sp Pif1 In Complex With Adp-alf4
Cell Rep (2016) 14 p.2030-2039
Pif1 is a conserved SF1B DNA helicase involved in maintaining genome stability through unwinding double-stranded DNAs (dsDNAs), DNA/RNA hybrids, and G quadruplex (G4) structures. Here, we report the structures of the helicase domain of human Pif1 and Bacteroides sp Pif1 (BaPif1) in complex with ADP-AlF4(-) and two different single-stranded DNAs (ssDNAs). The wedge region equivalent to the beta hairpin in other SF1B DNA helicases folds into an extended loop followed by an alpha helix. The Pif1 signature motif of BaPif1 interacts with the wedge region and a short helix in order to stabilize these ssDNA binding elements, therefore indirectly exerting its functional role. Domain 2B of BaPif1 undergoes a large conformational change upon concomitant binding of ATP and ssDNA, which is critical for Pif1's activities. BaPif1 cocrystallized with a tailed dsDNA and ADP-AlF4(-), resulting in a bound ssDNA bent nearly 90 degrees at the ssDNA/dsDNA junction. The conformational snapshots of BaPif1 provide insights into the mechanism governing the helicase activity of Pif1.