Exploitation of a virus-borne small protein to combat antibiotic resistance in Staphylococcus aureus




01. July 2019 - 31. December 2022


0,11 FTE


Janez Mravljak


4.06.04 Biotechnical sciences/Biotechnology/Microbe biotechnology

Research Organisation:







The development of drug‑resistant bacteria is an unavoidable outcome of widespread antibacterial chemotherapy of infectious diseases. Drug discovery programs directed against proteins considered essential for in vivo bacterial viability have yielded few new therapeutic classes of antibiotics, therefore treatment options for combating bacteria resistant to multiple drugs are narrowing. Hence, novel strategies to fight bacterial pathogens are urgently needed. Adaptation of bacteria to antibiotic therapy requires specific biochemical processes that may be subject to intervention. Preventing bacteria to acquire resistance to antibiotics will significantly prolong the lifetime of current‑day antibiotics. We will achieve this by an innovative strategy, with novel drugs that block antibiotic stress and resistance development in bacteria, prolonging the efficacy of licensed antibiotics. Clinically significant antibiotics induce mechanisms in pathogenic bacteria that activate the DNA damage response, designated the SOS response. Antibiotic‑induced SOS responses can (i) modulate the evolution and spread of drug resistance as well as virulence factors in pathogens, (ii) induce mutations and generate antibiotic resistance during therapy, (iii) induce persistence and multidrug tolerance in a subpopulation of bacterial cells that are not heritably resistant, (iv) induce biofilm formation and (v) toxin synthesis. The importance of regulating responses to stress suggests that modulation of SOS induction has the potential to address the problem of evolution of antibiotic resistance at its roots. Experimentally inactivating transcription factor LexA, the key regulator of the response, renders the bacteria unable to initiate the SOS response, these strains are sensitized to genotoxic antimicrobials and exhibit decreased mutation rates. The natural products synthesized by microorganisms are privileged compounds for the discovery of antibiotics as they result from natural selection and are the source of highly effective antibiotics. Our recent results reported the discovery of a small, 50-residue bacteriophage protein, gp7, able to interact with and modulate functions of the global transcription factor LexA, a key SOS regulator involved in the development of antibiotic resistance. This is the first report of a natural molecule that interacts directly with LexA to inhibit its self-cleavage activity and enhance its DNA binding, thus inhibit the host SOS response. We obtained the crystal structure of the gp7 protein and according to SAXS data we generated a structural model of gp7 in complex with LexA. Based on the unpublished structures we aim to obtain few high-affinity LexA-inhibitory lead compounds or gp7 derivatives, that will after optimisation give rise to a safe “anti-evolutionary” therapeutics, to be used in combination with licensed antibiotics to fight Bacillus sp. and Staphlococcus aureus infections. First we will enhance our knowledge on biology of gp7 protein in vitro and on the genome-wide scale in Bacillus and Staphylococcus sp. This will enable us to better understand gp7-driven processes in the cell which is essential to be able to generate a safe anti-evolutionary therapeutics. Next, we will use computer-assisted drug design based on the gp7 protein characteristics to select for the chemical libraries which will be assayed for the Bacillus sp. and the S. aureus LexA self-cleavage inhibitors. This will provide us with lead SOS inhibitor structures to block mechanisms enabling resistance. We will determine the equilibrium dissociation constants for the leads-LexA interaction and evaluate the antibiotic-potentiated activity of molecules targeting LexA by assaying the inhibition of the antibiotic resistance accumulation in Bacillus sp. and in S. aureus. We believe that optimised leads/gp7-derivatives in combination with current‑day, licensed antibiotics will assist in the battle against the development of antibiotic resistance.



Bibliographical references, arising directly from the implementation of the project:


Financed by:

Research projects (co)funded by the Slovenian Research Agency.