The T4 Phage DNA Mimic Protein Arn Inhibits the DNA Binding Activity of the Bacterial Histone-like Protein H-NS

Chun-Han Ho; Hao-Ching Wang; Tzu-Ping Ko; Yuan-Chih Chang; Andrew H.-J. Wang

doi:10.1074/jbc.M114.590851

The T4 Phage DNA Mimic Protein Arn Inhibits the DNA Binding Activity of the Bacterial Histone-like Protein H-NS*

From the ^‡Institute of Biochemical Sciences, National Taiwan University, Taipei 106, Taiwan,
^§Institute of Biological Chemistry,
^‖Core Facilities for Protein Structural Analysis, and
^**Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 115, Taiwan, and
^¶Graduate Institute of Translational Medicine, College of Medical Science and Technology, Taipei Medical University, Taipei 110, Taiwan

↵1 To whom correspondence should be addressed: Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan. Tel.: 886-2-2788-1981; Fax: 886-2-2788-2043; E-mail: ahjwang{at}gate.sinica.edu.tw.

Background: DNA mimic proteins prevent DNA-binding proteins from binding to DNA.

Results: T4 phage DNA mimic protein Arn disrupts H-NS·DNA binding and neutralizes the gene-silencing effect of H-NS.

Conclusion: Arn participates in viral anti-host defense system by its DNA mimicking properties.

Significance: This anti-H-NS function of Arn represents a novel battle mechanism between phage and bacteria.

Abstract

The T4 phage protein Arn (Anti restriction nuclease) was identified as an inhibitor of the restriction enzyme McrBC. However, until now its molecular mechanism remained unclear. In the present study we used structural approaches to investigate biological properties of Arn. A structural analysis of Arn revealed that its shape and negative charge distribution are similar to dsDNA, suggesting that this protein could act as a DNA mimic. In a subsequent proteomic analysis, we found that the bacterial histone-like protein H-NS interacts with Arn, implying a new function. An electrophoretic mobility shift assay showed that Arn prevents H-NS from binding to the Escherichia coli hns and T4 p8.1 promoters. In vitro gene expression and electron microscopy analyses also indicated that Arn counteracts the gene-silencing effect of H-NS on a reporter gene. Because McrBC and H-NS both participate in the host defense system, our findings suggest that T4 Arn might knock down these mechanisms using its DNA mimicking properties.

Footnotes

↵* This work was supported by the Core Facilities for Protein Structural Analysis funded by National Core Facilities Program for Biotechnology (NSC 100-2325-B-001-029 and NSC 101-2319-B-001-003).
The atomic coordinates and structure factors (code 3WX4) have been deposited in the Protein Data Bank (http://wwpdb.org/).