Abstract
RecQ helicases are important maintainers of genome integrity with distinct roles in almost every cellular process requiring access to DNA. RECQL5 is one of five human RecQ proteins and is particularly versatile in this regard, forming protein complexes with a diverse set of cellular partners in order to coordinate its helicase activity to various processes including replication, recombination and DNA repair. In this study, we have determined crystal structures of the core helicase domain of RECQL5 both with and without the nucleotide ADP in two distinctly different (‘Open’ and ‘Closed’) conformations. Small angle X-ray scattering studies show that the ‘Open’ form of the protein predominates in solution and we discuss implications of this with regards to the RECQL5 mechanism and conformational changes. We have measured the ATPase, helicase and DNA binding properties of various RECQL5 constructs and variants and discuss the role of these regions and residues in the various RECQL5 activities. Finally, we have performed a systematic comparison of the RECQL5 structures with other RecQ family structures and based on these comparisons we have constructed a model for the mechano-chemical cycle of the common catalytic core of these helicases.
Highlights
RECQL5 is a member of the RecQ family of helicases, which are highly conserved throughout evolution [1], and function in many diverse cellular processes with the role of maintaining genome integrity
Crystals were obtained for the APO protein which diffracted to a maximum resolution of 3.2 A, and the structure was solved by molecular replacement using the structure of BLM helicase as a search model [32], with two chains in the asymmetric unit
We have characterized RECQL5 binding to various DNA substrates and show a fairly strong preference for binding splayed arm or looped duplex DNA structures, both of which are implicated in transcription
Summary
RECQL5 ( known as RECQ5) is a member of the RecQ family of helicases, which are highly conserved throughout evolution [1], and function in many diverse cellular processes with the role of maintaining genome integrity. Whilst no specific human disease has been associated with mutations in RECQL5, polymorphisms have been associated with increased incidence of cancer in human populations [5,6], and knockout studies in mice show increased cancer susceptibility and greater incidence of double strand breaks and sister chromatid exchanges [7]. Consistent with this it has been suggested that RECQL5 plays a general role in cells as a tumor suppressor and maintainer of genome integrity.
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