title: Kinetic mechanism of DNA unwinding by the BLM helicase core and molecular basis for its low processivity.
abstract: Bloom's syndrome (BS) is a rare human autosomal recessive disorder characterized by a strong predisposition to a wide range of cancers commonly affecting the general population. Understanding the functioning mechanism of the BLM protein may provide the opportunity to develop new effective therapy strategies. In this work, we studied the DNA unwinding kinetic mechanism of the helicase core of the BLM protein using various stopped-flow assays. We show that the helicase core of BLM unwinds duplex DNA as monomers even under conditions strongly favoring oligomerization. An unwinding rate of approximately 20 steps per second and a step size of 1 bp have been determined. We have observed that the helicase has a very low processivity. From dissociation and inhibition experiments, we have found that during its ATP hydrolysis cycle in DNA unwinding the helicase tends to dissociate from the DNA substrate in the ADP state. The experimental results imply that the BLM helicase core may unwind duplex DNA in an inchworm manner.
authors.affiliation: Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Ye
authors.initials: Y
authors.lastname: Yang
authors.forename: Shuo-Xing
authors.initials: SX
authors.lastname: Dou
authors.forename: Ya-Nan
authors.initials: YN
authors.lastname: Xu
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bazeille
authors.forename: Peng-Ye
authors.initials: PY
authors.lastname: Wang
authors.forename: Pascal
authors.initials: P
authors.lastname: Rigolet
authors.forename: Hou-Qiang
authors.initials: HQ
authors.lastname: Xu
authors.forename: Xu Guang
authors.initials: XG
authors.lastname: Xi
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D001665:Binding Sites; D001816:Bloom Syndrome / Q000201:enzymology / Q000378:metabolism; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D019281:Dimerization; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D053484:RecQ Helicases / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D004247:DNA; C097151:Bloom syndrome protein; D053484:RecQ Helicases