Plasmid replication initiator RepB forms a hexamer reminiscent of ring helicases and has mobile nuclease domains.
RepB initiates plasmid rolling-circle replication by binding to a triple 11-bp direct repeat (bind locus) and cleaving the DNA at a specific distant site located in a hairpin loop within the nic locus of the origin. The structure of native full-length RepB reveals a hexameric ring molecule, where each protomer has two domains. The origin-binding and catalytic domains show a three-layer alpha-beta-alpha sandwich fold. The active site is positioned at one of the faces of the beta-sheet and coordinates a Mn2+ ion at short distance from the essential nucleophilic Y99. The oligomerization domains (ODs), each consisting of four alpha-helices, together define a compact ring with a central channel, a feature found in ring helicases. The toroidal arrangement of RepB suggests that, similar to ring helicases, it encircles one of the DNA strands during replication to confer processivity to the replisome complex. The catalytic domains appear to be highly mobile with respect to ODs. This mobility may account for the adaptation of the protein to two distinct DNA recognition sites.
Institute for Research in Biomedicine, Barcelona Science Park, Barcelona, Spain.
D Roeland
DR
Boer
José A
JA
Ruíz-Masó
José R
JR
López-Blanco
Alexander G
AG
Blanco
Mireia
M
Vives-Llàcer
Pablo
P
Chacón
Isabel
I
Usón
F Xavier
FX
Gomis-Rüth
Manuel
M
Espinosa
Oscar
O
Llorca
Gloria
G
del Solar
Miquel
M
Coll
D000595:Amino Acid Sequence; D001665:Binding Sites; D020134:Catalytic Domain; D004265:DNA Helicases / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry*
D021122:Protein Subunits; C106846:RepB helicase; D004265:DNA Helicases