title: Multimeric BLM is dissociated upon ATP hydrolysis and functions as monomers in resolving DNA structures.
abstract: Bloom (BLM) syndrome is an autosomal recessive disorder characterized by an increased risk for many types of cancers. Previous studies have shown that BLM protein forms a hexameric ring structure, but its oligomeric form in DNA unwinding is still not well clarified. In this work, we have used dynamic light scattering and various stopped-flow assays to study the active form and kinetic mechanism of BLM in DNA unwinding. It was found that BLM multimers were dissociated upon ATP hydrolysis. Steady-state and single-turnover kinetic studies revealed that BLM helicase always unwound duplex DNA in the monomeric form under conditions of varying enzyme and ATP concentrations as well as 3'-ssDNA tail lengths, with no sign of oligomerization being discerned. Measurements of ATPase activity further indicated that BLM helicase might still function as monomers in resolving highly structured DNAs such as Holliday junctions and D-loops. These results shed new light on the underlying mechanism of BLM-mediated DNA unwinding and on the molecular and functional basis for the phenotype of heterozygous carriers of BLM syndrome.
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and CAS Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Ya-Nan
authors.initials: YN
authors.lastname: Xu
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bazeille
authors.forename: Xiu-Yan
authors.initials: XY
authors.lastname: Ding
authors.forename: Xi-Ming
authors.initials: XM
authors.lastname: Lu
authors.forename: Peng-Ye
authors.initials: PY
authors.lastname: Wang
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Bugnard
authors.forename: Virginie
authors.initials: V
authors.lastname: Grondin
authors.forename: Shuo-Xing
authors.initials: SX
authors.lastname: Dou
authors.forename: Xu Guang
authors.initials: XG
authors.lastname: Xi
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D008027:Light; D055503:Protein Multimerization; D053484:RecQ Helicases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D012542:Scattering, Radiation
chemical_list: D000266:Adenylyl Imidodiphosphate; D000255:Adenosine Triphosphate; D004247:DNA; D000251:Adenosine Triphosphatases; C097151:Bloom syndrome protein; D053484:RecQ Helicases