Escherichia coli and other enteric bacteria are a major cause of human diseases. Biofilm formation contributes greatly to bacterial persistence and antimicrobial resistance in the host. Many enteric bacteria, including E. coli, produce functional amyloid fibers called curli as a major proteinaceous component of their extracellular matrix. It is now clear that functional amyloids are widespread, with examples found throughout cellular life. The curli system in E. coli provides a rich and high throughput genetic and biochemical toolbox for the study of amyloid formation. We want to learn how E. coli controls curli amyloid formation with protein inhibitors and how we can interrogate curli amyloid formation with rationally-designed chemical chaperones. We hypothesize that E. coli utilizes periplasmic proteins to shuttle the curli subunits through the periplasmic space and to avoid inappropriate amyloid formation in the periplasm. We have identified two chaperone-like proteins in the E. coli periplasm for which we will characterize the molecular mechanism of their amyloid inhibitory activity. We will also use rationally-designed small molecules to investigate the biochemical stage(s) at which curli amyloid formation can be stopped. Knowledge gained from the following experiments will have implications for microbial pathogenesis, general protein folding, and amyloid biogenesis, thus paving the way for new therapies that rationally target these critical biological processes. Our previous discoveries have contributed to a curli assembly model where the main fiber component CsgA and the minor subunit CsgB are secreted through the outer membrane via the lipoprotein CsgG. CsgB attaches to the surface of the cell and templates the folding of CsgA into an amyloid fiber. CsgE, an accessory protein with chaperone-like activity against CsgA, is also required for curli subunit secretion. CsgA subunits that might inappropriately polymerize in the periplasm are inhibited from amyloid accumulation via CsgC. In order to rationally develop therapeutics against amyloid assembly and amyloid-dependent biofilm formation, we must better understand curli biogenesis and its function in biofilm development.
In Aim 1 the coordinated roles of the chaperone-like protein CsgE and the outer membrane lipoprotein CsgG in directing efficient CsgA transport through the periplasm will be explored. We will also determine not only how CsgE interacts with CsgA and other amyloidogenic proteins but also the consequences of these interactions.
In Aim 2 we will characterize the interaction and specificity of the potent anti-amyloid factor CsgC. We will determine how CsgC functions to inhibit CsgA and ?-synuclein polymerization at low stoichiometric ratios. Finally, in Aim 3 we will characterize small molecules with amyloid-inhibiting capabilities. In collaboration with Fredrik Almqvist at Ume University in Sweden, we have already identified molecules that discourage CsgA polymerization. We will further characterize how these peptidomimetic compounds inhibit amyloid polymerization, assess their specificity, and test for their ability to inhibit biofilm formation.
Escherichia coli and related enteric bacteria are a major causative agent of infections worldwide. During pathogenesis, E. coli enters into a protective biofilm state that can resist host immune defenses and antibiotic therapies. We propose to determine how E. coli assembles and utilizes a critical biofilm determinant called curli to inspire new approaches for combating infectious disease.
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