The Functional Curli Amyloid Is Not Based on In-register Parallel β-Sheet Structure

Frank Shewmaker,Ryan P Mcglinchey,Kent R Thurber,Peter Mcphie,Fred Dyda,Robert Tycko,Reed B Wickner

doi:10.1074/jbc.m109.007054

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-beta structure that distinguishes protein amyloid. However, solid state NMR experiments indicate that curli structure is not based on an in-register parallel beta-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 a beta-helix-like structure but are not sufficient to establish such a structure definitively.

Highlights

Interest in amyloid is largely because of its association with many late onset human diseases, including Alzheimer disease (A␤),2 Parkinson disease (␣-synuclein), type II diabetes, and the transmissible spongiform encephalopathies (PrP)
The term amyloid has come to mean a filamentous protein aggregate with cross-␤ secondary structure and protease resistance
After CsgA samples were removed from denaturing conditions and incubated in non-denaturing buffer, small fibrils formed within 1 day, and larger filamentous networks formed over subsequent days as observed by electron microscopy (Fig. 1C and supplemental Fig. 1)

Summary

Introduction

Interest in amyloid is largely because of its association with many late onset human diseases, including Alzheimer disease (A␤),2 Parkinson disease (␣-synuclein), type II diabetes (amylin), and the transmissible spongiform encephalopathies (PrP). We confirm that the fibrils formed in vitro by CsgA and CsgB proteins are amyloids and explore their structure using solid state NMR and electron microscopy.

Results

Conclusion