The functional curli amyloid is not based on in-register parallel β-sheet structure

Abstract

The extracellular curli proteins of Enterobacteriaceae form fibrous structures that are involved in biofilm formation and adhesion to host cells. These curli fibrils are considered a functional amyloid because they are not a consequence of misfolding, but they have many of the properties of protein amyloid. We confirm that fibrils formed by CsgA and CsgB, the primary curli proteins of Escherichia coli, possess many of the hallmarks typical of amyloid. Moreover we demonstrate that curli fibrils possess the cross-β structure that distinguishes protein amyloid. However, solid stateNMRexperiments indicate that curli structure is not based on an in-register β-sheet architecture, which is common to many human disease-associated amyloids and the yeast prion amyloids. Solid state NMR and electron microscopy data are consistent with β-helix-like structure but are not sufficient to establish such a structure definitively. © 2009 by The American Society for Biochemistry and Molecular Biology, Inc.