Suramin is a potent and selective inhibitor of Mycobacterium tuberculosis RecA protein and the SOS response: RecA as a potential target for antibacterial drug discovery.
OBJECTIVE
In eubacteria, RecA is essential for recombinational DNA repair and for stalled replication forks to resume DNA synthesis. Recent work has implicated a role for RecA in the development of antibiotic resistance in pathogenic bacteria. Consequently, our goal is to identify and characterize small-molecule inhibitors that target RecA both in vitro and in vivo.


METHODS
We employed ATPase, DNA strand exchange and LexA cleavage assays to elucidate the inhibitory effects of suramin on Mycobacterium tuberculosis RecA. To gain insights into the mechanism of suramin action, we directly visualized the structure of RecA nucleoprotein filaments by atomic force microscopy. To determine the specificity of suramin action in vivo, we investigated its effect on the SOS response by pull-down and western blot assays as well as for its antibacterial activity.


RESULTS
We show that suramin is a potent inhibitor of DNA strand exchange and ATPase activities of bacterial RecA proteins with IC(50) values in the low micromolar range. Additional evidence shows that suramin inhibits RecA-catalysed proteolytic cleavage of the LexA repressor. The mechanism underlying such inhibitory actions of suramin involves its ability to disassemble RecA-single-stranded DNA filaments. Notably, suramin abolished ciprofloxacin-induced recA gene expression and the SOS response and augmented the bactericidal action of ciprofloxacin.


CONCLUSIONS
Our findings suggest a strategy to chemically disrupt the vital processes controlled by RecA and hence the promise of small molecules for use against drug-susceptible as well as drug-resistant strains of M. tuberculosis for better infection control and the development of new therapies.
Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India.
Astha
A
Nautiyal
Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India.
K Neelakanteshwar
KN
Patil
Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India kmbc@biochem.iisc.ernet.in.
K
K
Muniyappa
D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors; D000995:Antitubercular Agents / Q000378:metabolism*; D055808:Drug Discovery; D006801:Humans; D020128:Inhibitory Concentration 50; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000201:enzymology*; D011480:Protease Inhibitors / Q000378:metabolism; D011938:Rec A Recombinases / Q000037:antagonists & inhibitors*; D013014:SOS Response, Genetics / Q000187:drug effects*; D013498:Suramin / Q000378:metabolism*
D000995:Antitubercular Agents; D011480:Protease Inhibitors; D013498:Suramin; D011938:Rec A Recombinases; D000251:Adenosine Triphosphatases
LexA repressor; RecA nucleoprotein filaments; antibiotic resistance; recombinational DNA repair