A prominent ?-hairpin structure in the winged-helix domain of RECQ1 is required for DNA unwinding and oligomer formation.

ABSTRACT: RecQ helicases have attracted considerable interest in recent years due to their role in the suppression of genome instability and human diseases. These atypical helicases exert their function by resolving a number of highly specific DNA structures. The crystal structure of a truncated catalytic core of the human RECQ1 helicase (RECQ1(49-616)) shows a prominent ?-hairpin, with an aromatic residue (Y564) at the tip, located in the C-terminal winged-helix domain. Here, we show that the ?-hairpin is required for the DNA unwinding and Holliday junction (HJ) resolution activity of full-length RECQ1, confirming that it represents an important determinant for the distinct substrate specificity of the five human RecQ helicases. In addition, we found that the ?-hairpin is required for dimer formation in RECQ1(49-616) and tetramer formation in full-length RECQ1. We confirmed the presence of stable RECQ1(49-616) dimers in solution and demonstrated that dimer formation favours DNA unwinding; even though RECQ1 monomers are still active. Tetramers are instead necessary for more specialized activities such as HJ resolution and strand annealing. Interestingly, two independent protein-protein contacts are required for tetramer formation, one involves the ?-hairpin and the other the N-terminus of RECQ1, suggesting a non-hierarchical mechanism of tetramer assembly.

SUBMITTER: Lucic B 

PROVIDER: S-EPMC3061051 | biostudies-literature | 2011 Mar

REPOSITORIES: biostudies-literature