E. coli produce extracellular fibers termed curli that contribute to bacterial adhesion and biofilm formation. Since the recent discovery in 2002 that curli fibers were amyloid, additional functional amyloids have been discovered. This awareness has prompted an increase in the appreciation of the prevalent and crucial role that amyloids play in bacterial colonization and persistence. The non-crystalline and insoluble nature of amyloids including curli poses challenges to their analysis. Solid-state NMR is uniquely suited to study amyloids because it can provide quantitative information about connectivity and spatial contacts and does not require high quality crystals (x-ray crystallography) or high tumbling rates in solution (solution NMR). We have employed solid-state NMR as well as complementary biochemical techniques such as dark-field transmission electron microscopy and fluorescence microscopy to analyze the native curli structure as well as to gain an understanding of how curli fibers interact with amyloid dyes and additional biofilm matrix components. Towards generating a molecular model of the curli fiber, we have identified several key distances between inter-strand residues in selectively and uniformly-13C, 15N labeled curli samples using REDOR and frequency-selective REDOR. A better understanding of curli, how they are formed, and their biological role will help us to understand the assembly of microbial amyloids and their functions including how they contribute to the assembly of biofilms.

Curli: Functional bacterial amyloid fibers

249th National Meeting (2015)

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