Nucleic Acids Research Advance Access published online on September 16, 2009
Nucleic Acids Research, doi:10.1093/nar/gkp756
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Structural Biology |
The Staphylococcus aureus pSK41 plasmid-encoded ArtA protein is a master regulator of plasmid transmission genes and contains a RHH motif used in alternate DNA-binding modes
1Department of Biochemistry and Molecular Biology, University of Texas, M.D. Anderson Cancer Center, Unit 1000, Houston, TX 77030, USA, 2School of Biological Sciences, University of Sydney, Sydney, New South Wales 2006 and 3School of Biological Sciences, Flinders University, Adelaide, South Australia, Australia
*To whom correspondence should be addressed. Tel: +1 713 834 6392; Fax: +1 713 834 6397; Email: maschuma{at}mdanderson.org.
Received July 29, 2009. Revised August 24, 2009. Accepted August 27, 2009.
Plasmids harbored by Staphylococcus aureus are a major contributor to the spread of bacterial multi-drug resistance. Plasmid conjugation and partition are critical to the dissemination and inheritance of such plasmids. Here, we demonstrate that the ArtA protein encoded by the S. aureus multi-resistance plasmid pSK41 is a global transcriptional regulator of pSK41 genes, including those involved in conjugation and segregation. ArtA shows no sequence homology to any structurally characterized DNA-binding protein. To elucidate the mechanism by which it specifically recognizes its DNA site, we obtained the structure of ArtA bound to its cognate operator, ACATGACATG. The structure reveals that ArtA is representative of a new family of ribbon–helix–helix (RHH) DNA-binding proteins that contain extended, N-terminal basic motifs. Strikingly, unlike most well-studied RHH proteins ArtA binds its cognate operators as a dimer. However, we demonstrate that it is also able to recognize an atypical operator site by binding as a dimer-of-dimers and the extended N-terminal regions of ArtA were shown to be essential for this dimer-of-dimer binding mode. Thus, these data indicate that ArtA is a master regulator of genes critical for both horizontal and vertical transmission of pSK41 and that it can recognize DNA utilizing alternate binding modes.
The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors.