A Diversity of Assembly Mechanisms of a Generic Amyloid Fold

Eichner, Timo; Radford, Sheena E.

doi:10.1016/j.molcel.2011.05.012

Cited by 272 publications

(276 citation statements)

References 119 publications

(180 reference statements)

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“…Some intrinsically disordered proteins may initially form amorphous aggregates, and the amyloid assemblies (fibers) emerge exclusively from within the aggregates, as reported by others (29). Polymorphism of amyloid has been widely observed (30,31).…”

Section: Discussionmentioning

confidence: 61%

The E. coli CsgB nucleator of curli assembles to β-sheet oligomers that alter the CsgA fibrillization mechanism

Crick

Pinkner

Ford

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Curli are extracellular proteinaceous functional amyloid aggregates produced by Escherichia coli , Salmonella spp., and other enteric bacteria. Curli mediate host cell adhesion and invasion and play a critical role in biofilm formation. Curli filaments consist of CsgA, the major subunit, and CsgB, the minor subunit. In vitro, purified CsgA and CsgB exhibit intrinsically disordered properties, and both are capable of forming amyloid fibers similar in morphology to those formed in vivo. However, in vivo, CsgA alone cannot form curli fibers, and CsgB is required for filament growth. Thus, we studied the aggregation of CsgA and CsgB both alone and together in vitro to investigate the different roles of CsgA and CsgB in curli formation. We found that though CsgA and CsgB individually are able to self-associate to form aggregates/fibrils, they do so using different mechanisms and with different kinetic behavior. CsgB rapidly forms structured oligomers, whereas CsgA aggregation is slower and appears to proceed through large amorphous aggregates before forming filaments. Substoichiometric concentrations of CsgB induce a change in the mechanism of CsgA aggregation from that of forming amorphous aggregates to that of structured intermediates similar to those of CsgB alone. Oligomeric CsgB accelerated the aggregation of CsgA, in contrast to monomeric CsgB, which had no effect. The structured β-strand oligomers formed by CsgB serve as nucleators for CsgA aggregation. These results provide insights into the formation of curli in vivo, especially the nucleator function of CsgB.

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Section: Discussionmentioning

confidence: 61%

The E. coli CsgB nucleator of curli assembles to β-sheet oligomers that alter the CsgA fibrillization mechanism

Crick

Pinkner

Ford

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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“…As proposed for other amyloid-forming proteins (20,47), a conformational change in the protein monomer is thought to expose a previously buried segment that is prone to cross-β stacking, leaving the bulk of the native fold of the protein largely unchanged. These conformational change models were designed to describe the behavior of proteins that "switch" to an amyloidogenic state due to a localized conformational change under appropriate conditions.…”

Section: Discussionmentioning

confidence: 99%

Self-assembly of functional, amphipathic amyloid monolayers by the fungal hydrophobin EAS

Macindoe

Kwan

Ren

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

120

111

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The hydrophobin EAS from the fungus Neurospora crassa forms functional amyloid fibrils called rodlets that facilitate spore formation and dispersal. Self-assembly of EAS into fibrillar rodlets occurs spontaneously at hydrophobic:hydrophilic interfaces and the rodlets further associate laterally to form amphipathic monolayers. We have used site-directed mutagenesis and peptide experiments to identify the region of EAS that drives intermolecular association and formation of the cross-β rodlet structure. Transplanting this region into a nonamyloidogenic hydrophobin enables it to form rodlets. We have also determined the structure and dynamics of an EAS variant with reduced rodlet-forming ability. Taken together, these data allow us to pinpoint the conformational changes that take place when hydrophobins self-assemble at an interface and to propose a model for the amphipathic EAS rodlet structure.A myloid fibrils were first identified in association with human diseases, but recent discoveries show that the amyloid ultrastructure also contributes to important functions in normal biology (1, 2). In bacteria, fungi, insects, fish, and mammals, amyloid structures perform a wide variety of roles (3). Functional amyloids in the form of fibrillar rodlets composed of class I hydrophobin proteins are found in filamentous fungi. These hydrophobins are small proteins that are secreted as monomers and self-assemble into rodlets that pack to form amphipathic monolayers at hydrophilic: hydrophobic boundaries, such as the surface of the growth medium (4). These proteins are extremely surface active and lower the surface tension of the aqueous growth medium, allowing hyphae to break through the surface and to produce aerial structures (5, 6). Many of these aerial structures subsequently become coated with amyloid rodlets, creating a hydrophobic layer that serves multiple purposes, including conferring water resistance to spores for easier dispersal in air (7), preventing wetting or collapse of gas transfer channels (8), enhancing adherence to waxy surfaces such as leaves during infection of rice plants by Magnaporthe grisea (9), and mediating evasion of the immune system as is observed in Aspergillus fumigatus infections (10).Hydrophobins are characterized by the presence of eight cysteine residues that form four disulphide bonds, but the hydrophobin family can be further divided into two classes based on the spacing of the conserved cysteine residues and the nature of the amphipathic monolayers that they form (11). Class I, but not class II, hydrophobins form amyloid-like rodlets that are extremely robust and require treatment with strong acid to induce depolymerization. The amphipathic monolayers formed by class II hydrophobins are not fibrillar and can be dissociated by treatment with detergent and alcohol solutions. The soluble, monomeric forms of hydrophobins share a unique β-barrel topology, and all have a relatively large exposed hydrophobic area on the protein monomer surface (4). The diversity in sequence and chain length ...

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“…The molecular mechanisms underlying the lag phase-and nonlag phase-dependent kinetic routes and morphological features of protein aggregation are not fully understood (Uversky 2010;Eichner and Radford 2011a).…”

Section: Introductionmentioning

confidence: 99%

Application and use of differential scanning calorimetry in studies of thermal fluctuation associated with amyloid fibril formation

Sasahara

Goto

2012

Biophys Rev

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The aggregation of proteins into amyloid fibrils is a topic that has attracted great interest because the process is associated with the pathology of numerous human diseases. Despite considerable progress in the elucidation of the structure of amyloid fibrils and the kinetic mechanism of their formation, knowledge on the thermodynamic aspects underlying the formation and stability of amyloid fibrils is limited. In this review, we summarize recent calorimetric studies of amyloid fibril formation, with the goal of obtaining a better understanding of the causal factors that thermally induce proteins to aggregate into amyloid fibrils. Calorimetric data show that differential scanning calorimetry is a useful technique to study the causative factors that thermally trigger the conversion to the amyloid structure and highlight the physics related to the thermal fluctuation of proteins during this conversion.

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A Diversity of Assembly Mechanisms of a Generic Amyloid Fold

Cited by 272 publications

References 119 publications

The E. coli CsgB nucleator of curli assembles to β-sheet oligomers that alter the CsgA fibrillization mechanism

The E. coli CsgB nucleator of curli assembles to β-sheet oligomers that alter the CsgA fibrillization mechanism

Self-assembly of functional, amphipathic amyloid monolayers by the fungal hydrophobin EAS

Application and use of differential scanning calorimetry in studies of thermal fluctuation associated with amyloid fibril formation

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