Unique Helicase Determinants in the Essential Conjugative TraI Factor from Salmonella enterica Serovar Typhimurium Plasmid pCU1

Journal Article · Mon Jun 16 04:00:00 EDT 2014 · Journal of Bacteriology

DOI:https://doi.org/10.1128/JB.01496-14· OSTI ID:1347006

McLaughlin, K. J.; Nash, R. P.; Redinbo, M. R.

The widespread development of multidrug-resistant bacteria is a major health emergency. Conjugative DNA plasmids, which harbor a wide range of antibiotic resistance genes, also encode the protein factors necessary to orchestrate the propagation of plasmid DNA between bacterial cells through conjugative transfer. Successful conjugative DNA transfer depends on key catalytic components to nick one strand of the duplex DNA plasmid and separate the DNA strands while cell-to-cell transfer occurs. The TraI protein from the conjugative Salmonella plasmid pCU1 fulfills these key catalytic roles, as it contains both single-stranded DNA-nicking relaxase and ATP-dependent helicase domains within a single, 1,078-residue polypeptide. In this work, we unraveled the helicase determinants of Salmonella pCU1 TraI through DNA binding, ATPase, and DNA strand separation assays. TraI binds DNA substrates with high affinity in a manner influenced by nucleic acid length and the presence of a DNA hairpin structure adjacent to the nick site. TraI selectively hydrolyzes ATP, and mutations in conserved helicase motifs eliminate ATPase activity. Surprisingly, the absence of a relatively short (144-residue) domain at the extreme C terminus of the protein severely diminishes ATP-dependent strand separation. Collectively, these data define the helicase motifs of the conjugative factor TraI from Salmonella pCU1 and reveal a previously uncharacterized C-terminal functional domain that uncouples ATP hydrolysis from strand separation activity.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: USDOE; NIH
• OSTI ID: 1347006
• Journal Information: Journal of Bacteriology, Journal Name: Journal of Bacteriology Journal Issue: 17 Vol. 196; ISSN 0021-9193
• Publisher: American Society for Microbiology
• Country of Publication: United States
• Language: ENGLISH

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