Structure of a four-way bridged ParB-DNA complex provides insight into P1 segrosome assembly.
The plasmid partition process is essential for plasmid propagation and is mediated by par systems, consisting of centromere-like sites and two proteins, ParA and ParB. In the first step of partition by the archetypical P1 system, ParB binds a complicated centromere-like site to form a large nucleoprotein segrosome. ParB is a dimeric DNA-binding protein that can bridge between both A-boxes and B-boxes located on the centromere. Its helix-turn-helix domains bind A-boxes and the dimer domain binds B-boxes. Binding of the first ParB dimer nucleates the remaining ParB molecules onto the centromere site, which somehow leads to the formation of a condensed segrosome superstructure. To further understand this unique DNA spreading capability of ParB, we crystallized and determined the structure of a 1:2 ParB-(142-333):A3-B2-box complex to 3.35A resolution. The structure reveals a remarkable four-way, protein-DNA bridged complex in which both ParB helix-turn-helix domains simultaneously bind adjacent A-boxes and the dimer domain bridges between two B-boxes. The multibridging capability and the novel dimer domain-B-box interaction, which juxtaposes the DNA sites close in space, suggests a mechanism for the formation of the wrapped solenoid-like segrosome superstructure. This multibridging capability of ParB is likely critical in its partition complex formation and pairing functions.
Schumacher
Maria A
MA
Department of Biochemistry and Molecular Biology, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA. maschuma@mdanderson
Mansoor
André
A
Funnell
Barbara E
BE
D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D004279:DNA, Viral / Q000737:chemistry* / Q000378:metabolism; D019281:Dimerization; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D014764:Viral Proteins / Q000737:chemistry* / Q000378:metabolism
D001426:Bacterial Proteins; D004279:DNA, Viral; D046912:Multiprotein Complexes; C121785:ParB protein, Enterobacteria phage P1; D014764:Viral Proteins; C052883:chromosome partition proteins, bacterial