Sequence-dependent base pair stepping dynamics in XPD helicase unwinding

eLife

Maria Spies¹  Zhi Qi²  Yann R Chemla³  Robert A Pugh⁴ 

[1] Howard Hughes Medical Institute, University of Winconsin-Madison, Madison, United States;Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, United States;Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, United States;Institute for Molecular Virology, University of Wisconsin-Madison, Madison, United States;

关键词: helicase;    Xeroderma pigmentosum group D helicase;    molecular motor;    DNA repair;    optical tweezer;    single molecule;   

DOI  :  10.7554/eLife.00334

来源: DOAJ

【 摘 要 】

Helicases couple the chemical energy of ATP hydrolysis to directional translocation along nucleic acids and transient duplex separation. Understanding helicase mechanism requires that the basic physicochemical process of base pair separation be understood. This necessitates monitoring helicase activity directly, at high spatio-temporal resolution. Using optical tweezers with single base pair (bp) resolution, we analyzed DNA unwinding by XPD helicase, a Superfamily 2 (SF2) DNA helicase involved in DNA repair and transcription initiation. We show that monomeric XPD unwinds duplex DNA in 1-bp steps, yet exhibits frequent backsteps and undergoes conformational transitions manifested in 5-bp backward and forward steps. Quantifying the sequence dependence of XPD stepping dynamics with near base pair resolution, we provide the strongest and most direct evidence thus far that forward, single-base pair stepping of a helicase utilizes the spontaneous opening of the duplex. The proposed unwinding mechanism may be a universal feature of DNA helicases that move along DNA phosphodiester backbones.

【 授权许可】

Unknown