title: A helical bundle in the N-terminal domain of the BLM helicase mediates dimer and potentially hexamer formation.
abstract: Helicases play a critical role in processes such as replication or recombination by unwinding double-stranded DNA; mutations of these genes can therefore have devastating biological consequences. In humans, mutations in genes of three members of the RecQ family helicases (blm,wrn, andrecq4) give rise to three strikingly distinctive clinical phenotypes: Bloom syndrome, Werner syndrome, and Rothmund-Thomson syndrome, respectively. However, the molecular basis for these varying phenotypic outcomes is unclear, in part because a full mechanistic description of helicase activity is lacking. Because the helicase core domains are highly conserved, it has been postulated that functional differences among family members might be explained by significant differences in the N-terminal domains, but these domains are poorly characterized. To help fill this gap, we now describe bioinformatics, biochemical, and structural data for three vertebrate BLM proteins. We pair high resolution crystal structures with SAXS analysis to describe an internal, highly conserved sequence we term the dimerization helical bundle in N-terminal domain (DHBN). We show that, despite the N-terminal domain being loosely structured and potentially lacking a defined three-dimensional structure in general, the DHBN exists as a dimeric structure required for higher order oligomer assembly. Interestingly, the unwinding amplitude and rate decrease as BLM is assembled from dimer into hexamer, and also, the stable DHBN dimer can be dissociated upon ATP hydrolysis. Thus, the structural and biochemical characterizations of N-terminal domains will provide new insights into how the N-terminal domain affects the structural and functional organization of the full BLM molecule.
authors.affiliation: From the College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Shi
authors.affiliation: From the College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China.
authors.forename: Wei-Fei
authors.initials: WF
authors.lastname: Chen
authors.affiliation: From the College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Zhang
authors.affiliation: From the College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China.
authors.forename: San-Hong
authors.initials: SH
authors.lastname: Fan
authors.affiliation: From the College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China.
authors.forename: Xia
authors.initials: X
authors.lastname: Ai
authors.affiliation: From the College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China.
authors.forename: Na-Nv
authors.initials: NN
authors.lastname: Liu
authors.affiliation: the Institut de Biochimie et Chimie des Protéines, CNRS UMR 5086, 7 Passage du Vercors, 69367 Lyon, France, and stephane.rety@ibcp.fr.
authors.forename: Stephane
authors.initials: S
authors.lastname: Rety
authors.affiliation: From the College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China, xxi01@ens-cachan.fr.|the Laboratoire de Biologie et Pharmacologie Appliquée, ENS de Cachan, Université Paris-Saclay, CNRS, 61 Avenue du Président Wilson, 94235 Cachan, France.
authors.forename: Xu-Guang
authors.initials: XG
authors.lastname: Xi
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000818:Animals; D030161:Avian Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002645:Chickens; D018360:Crystallography, X-Ray; D000072417:Protein Domains; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D053484:RecQ Helicases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D030161:Avian Proteins; D000255:Adenosine Triphosphate; C097151:Bloom syndrome protein; D053484:RecQ Helicases
keywords: DNA helicase; X-ray crystallography; dimerization helical bundle; enzyme kinetics; genetic disease; protein self-assembly; small angle X-ray scattering