Different quaternary structures of human RECQ1 are associated with its dual enzymatic activity

Laura Muzzolini, Fabienne Beuron, Ardan Patwardhan, Venkateswarlu Popuri, Sheng Cui, Benedetta Niccolini, Mathieu Rappas, Paul S. Freemont, Alessandro Vindigni

Research output: Contribution to journalArticlepeer-review

56 Scopus citations

Abstract

RecQ helicases are essential for the maintenance of chromosome stability. In addition to DNA unwinding, some RecQ enzymes have an intrinsic DNA strand annealing activity. The function of this dual enzymatic activity and the mechanism that regulates it is, however, unknown. Here, we describe two quaternary forms of the human RECQ1 helicase, higher-order oligomers consistent with pentamers or hexamers, and smaller oligomers consistent with monomers or dimers. Size exclusion chromatography and transmission electron microscopy show that the equilibrium between the two assembly states is affected by single-stranded DNA (ssDNA) and ATP binding, where ATP or ATPγS favors the smaller oligomeric form. Our three-dimensional electron microscopy reconstructions of human RECQ1 reveal a complex cage-like structure of approximately 120 Å X 3130 Å with a central pore. This oligomeric structure is stabilized under conditions in which RECQ1 is proficient in strand annealing. In contrast, competition experiments with the ATPase-deficient K119R and E220Q mutants indicate that RECQ1 monomers, or tight binding dimers, are required for DNA unwinding. Collectively, our findings suggest that higher-order oligomers are associated with DNA strand annealing, and lower-order oligomers with DNA unwinding.

Original languageEnglish
Pages (from-to)157-168
Number of pages12
JournalPLoS biology
Volume5
Issue number2
DOIs
StatePublished - Feb 2007

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