Screening for Inhibitors of the Sigma-E Pathway

Bacteria can rapidly modulate their envelope proteins in response to antibiotic exposure and host attack to greatly increase their resistance and survival. The σ^E cell envelope status-sensing pathway is the major pathway used by gram-negative pathogens to regulate their envelope proteins in response to stress. Here, we use two separate high-through-put screens to isolate inhibitors of the σ^E pathway from both a cyclic peptide library and a small molecule library.  The cyclic peptide screen is based on gain of fluorescence while the complementary small molecule screen uses gain of luminescence in the event of σ^E pathway inhibition.  Both utilize promoter fusions to induce constitutive activation of the σ^E pathway and translate end activity levels into a gain of signal. Inhibitors isolated from these screens could serve as lead compounds for novel antibiotics.  Additionally, σ^E pathway inhibitors would be extremely useful in future studies aiming to elucidate the σ^E pathway because knock-outs of σ^E acquire suppressor mutations in order to survive.