Nucleic Acids Research Advance Access published online on March 19, 2007
Nucleic Acids Research, doi:10.1093/nar/gkm077
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Molecular Biology |
The neutrophil-activating Dps protein of Helicobacter pylori, HP-NAP, adopts a mechanism different from Escherichia coli Dps to bind and condense DNA
1C.N.R. Institute of Molecular Biology and Pathology, Department of Biochemical Sciences ‘A. Rossi-Fanelli’, University of Rome ‘La Sapienza’, 00185 Rome, Italy and 2Department of Biochemistry and Molecular Biology, University of Parma, 43100 Parma, Italy
*To whom correspondence should be addressed. Tel: +39 06 4940543; +39 06 49910761; Fax: +39 06 4440062; Email: emilia.chiancone{at}uniroma1.it
Received December 21, 2006. Revised January 19, 2007. Accepted January 24, 2007.
The Helicobacter pylori neutrophil-activating protein (HP-NAP), a member of the Dps family, is a fundamental virulence factor involved in H.pylori-associated disease. Dps proteins protect bacterial DNA from oxidizing radicals generated by the Fenton reaction and also from various other damaging agents. DNA protection has a chemical component based on the highly conserved ferroxidase activity of Dps proteins, and a physical one based on the capacity of those Dps proteins that contain a positively charged N-terminus to bind and condense DNA. HP-NAP does not possess a positively charged N-terminus but, unlike the other members of the family, is characterized by a positively charged protein surface. To establish whether this distinctive property could be exploited to bind DNA, gel shift, fluorescence quenching and atomic force microscopy (AFM) experiments were performed over the pH range 6.5–8.5. HP-NAP does not self-aggregate in contrast to Escherichia coli Dps, but is able to bind and even condense DNA at slightly acid pH values. The DNA condensation capacity acts in concert with the ferritin-like activity and could be used to advantage by H.pylori to survive during host-infection and other stress challenges. A model for DNA binding/condensation is proposed that accounts for all the experimental observations.
The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors.
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