Format

Send to

Choose Destination
Proc Natl Acad Sci U S A. 2010 Jun 29;107(26):11763-8. doi: 10.1073/pnas.1003817107. Epub 2010 Jun 4.

Plasmid protein TubR uses a distinct mode of HTH-DNA binding and recruits the prokaryotic tubulin homolog TubZ to effect DNA partition.

Author information

1
Department of Biochemistry and Molecular Biology, University of Texas, M. D. Anderson Cancer Center, Unit 1000, Houston, TX 77030, USA.

Abstract

The segregation of plasmid DNA typically requires three elements: a DNA centromere site, an NTPase, and a centromere-binding protein. Because of their simplicity, plasmid partition systems represent tractable models to study the molecular basis of DNA segregation. Unlike eukaryotes, which utilize the GTPase tubulin to segregate DNA, the most common plasmid-encoded NTPases contain Walker-box and actin-like folds. Recently, a plasmid stability cassette on Bacillus thuringiensis pBtoxis encoding a putative FtsZ/tubulin-like NTPase called TubZ and DNA-binding protein called TubR has been described. How these proteins collaborate to impart plasmid stability, however, is unknown. Here we show that the TubR structure consists of an intertwined dimer with a winged helix-turn-helix (HTH) motif. Strikingly, however, the TubR recognition helices mediate dimerization, making canonical HTH-DNA interactions impossible. Mutagenesis data indicate that a basic patch, encompassing the two wing regions and the N termini of the recognition helices, mediates DNA binding, which indicates an unusual HTH-DNA interaction mode in which the N termini of the recognition helices insert into a single DNA groove and the wings into adjacent DNA grooves. The TubZ structure shows that it is as similar structurally to eukaryotic tubulin as it is to bacterial FtsZ. TubZ forms polymers with guanine nucleotide-binding characteristics and polymer dynamics similar to tubulin. Finally, we show that the exposed TubZ C-terminal region interacts with TubR-DNA, linking the TubR-bound pBtoxis to TubZ polymerization. The combined data suggest a mechanism for TubZ-polymer powered plasmid movement.

PMID:
20534443
PMCID:
PMC2900659
DOI:
10.1073/pnas.1003817107
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center