3m8k
Protein structure of type III plasmid segregation TubZ
Structural highlights
FunctionTUBZ_BACTI A tubulin-like, filament forming GTPase; the motor component of the type III plasmid partition system which ensures correct segregation of the pBtoxis plasmid. Filaments may seed from the centromere-like site (tubC) when bound by DNA-binding protein TubR; the tubC-TubR complex stabilizes the TubZ filament. Filaments grow at the plus end and depolymerize at the minus end, a process called treadmilling. TubR-tubC complexes track the depolymerizing minus end of the filament, probably pulling plasmid within the cell (PubMed:20534443, PubMed:23010931, PubMed:25825718). Required for pBtoxis plasmid replication/partition (PubMed:16936050, PubMed:17873046). Binds the TubR-tubC complex; GTP is not required for binding to TubR-tubC. TubZ alone does not bind DNA (PubMed:17873046, PubMed:20534443, PubMed:25825718). Has a high GTPase activity in the presence of Mg(2+); in the presence of GTP assembles into dynamic filaments which upon polymerization bind almost exclusively GDP. Filament formation is cooperative, requiring a critical concentration. Formation occurs very quickly and is followed by disassembly as GTP is consumed (PubMed:18198178).[1] [2] [3] [4] [5] [6] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe 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. Plasmid protein TubR uses a distinct mode of HTH-DNA binding and recruits the prokaryotic tubulin homolog TubZ to effect DNA partition.,Ni L, Xu W, Kumaraswami M, Schumacher MA Proc Natl Acad Sci U S A. 2010 Jun 4. PMID:20534443[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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