The Hydrophobin EAS Is Largely Unstructured in Solution and Functions by Forming Amyloid-Like Structures

Mackay, J.P.; Matthews, Jacqueline M.; Winefield, Robert D.; Mackay, Lindsey G.; Haverkamp, Richard G.; Templeton, Matthew D.

doi:10.1016/s0969-2126(00)00559-1

Cited by 139 publications

(124 citation statements)

References 46 publications

(10 reference statements)

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“…Several algorithms have been developed with the goal of predicting regions of protein sequence that have a high propensity for forming amyloid-like β-sheet polymeric structures. Given the evidence from X-ray fiber diffraction, electron microscopy, and Congo red and Thioflavin-T (ThT) binding that rodlets formed by class I hydrophobins are amyloid-like (15,16), we analyzed the amino acid sequence of EAS using several of these algorithms. TANGO (17) identified two potential aggregation-prone regions in EAS: residues L43-G51 and S71-A78 ( Fig.…”

Section: Resultsmentioning

confidence: 99%

“…The structures of EAS, EAS Δ15 and EAS Δ15 -F72G monomers all suggest that residues T66-S71, in the N-terminal half of the Cys7-Cys8 loop, are highly mobile in solution on the nanosecond time scale (15,16). Therefore, it is likely that a conformational change involving a larger proportion of the Cys7-Cys8 loop can take place upon contact with a suitable interface.…”

Section: Discussionmentioning

confidence: 99%

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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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Section: Resultsmentioning

confidence: 99%

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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“…In some cases, e.g., A␤, interfaces can give rise to alternative forms of fibrillar and nonfibrillar aggregates as determined by the nature of the interface (34). Finally, assembly of hydrophobins into functional amyloid-like rodlets occurs at an air-water interface (35). Thus, the choice of conditions is critical for understanding assembly.…”

Section: Discussionmentioning

confidence: 99%

Fiber-dependent amyloid formation as catalysis of an existing reaction pathway

Ruschak¹,

Miranker

2007

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

203

251

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A central component of a number of degenerative diseases is the deposition of protein as amyloid fibers. Self-assembly of amyloid occurs by a nucleation-dependent mechanism that gives rise to a characteristic sigmoidal reaction profile. The abruptness of this transition is a variable characteristic of different proteins with implications to both chemical mechanism and the aggressiveness of disease. Because nucleation is defined as the rate-limiting step, we have sought to determine the nature of this step for a model system derived from islet amyloid polypeptide. We show that nucleation occurs by two pathways: a fiber-independent (primary) pathway and a fiber-dependent (secondary) pathway. We first show that the balance between primary and secondary contributions can be manipulated by an external interface. Specifically, in the presence of this interface, the primary mechanism dominates, whereas in its absence, the secondary mechanism dominates. Intriguingly, we determine that both the reaction order and the enthalpy of activation of the two nucleation processes are identical. We interrogate this coincidence by global analysis using a simplified model generally applicable to protein polymerization. A physically reasonable set of parameters can be found to satisfy the coincidence. We conclude that primary and secondary nucleation need not represent different processes for amyloid formation. Rather, they are alternative manifestations of the same, surfacecatalyzed nucleation event.amylin ͉ fibers ͉ islet amyloid polypeptide ͉ nucleation T he noncovalent, fibrous self-assembly of proteins, including hemoglobin S, actin, microtubules, and amyloid fibers, occurs by a nucleation-dependent mechanism (1-5). If polymer product formation is monitored as a function of time in a reaction where all of the protein is initially monodisperse, there is a lag phase in which little product is formed, followed by a period of rapid growth (2). Such observations are consistent with a rate-limiting step in which change occurs to a high-energy intermediate known as the nucleus. In many systems such as actin, collagen, and microtubules, the nucleus is modeled as an oligomeric species that is in a highly unfavorable equilibrium with monomer (1, 3-6). The nucleus may also be a high-energy conformation of monomer, such as that reported for polyglutamine (7). Regardless, the rate-limiting step involves a nucleus because it is defined as the species with the highest free energy and therefore lowest population (1, 4).This model of nucleation alone cannot account for the high apparent cooperativity of conversion observed in many systems. Historically, hemoglobin S was the first biological polymerization reaction to demonstrate a transition time that is much shorter than its preceding lag phase (8). This same phenomenon is commonly reported for amyloid systems including islet amyloid polypeptide (IAPP) from type II diabetes (9), A␤ from Alzheimer's (10), PrP from the mammalian prion (11), and Sup35 from the yeast prion (12, 13), as well as mode...

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“…Nuclear Magnetic Resonance Spectroscopy-EAS ⌬15 isotopically labeled with 15 N was expressed and purified as described previously (16). 15 Circular Dichroism Spectropolariometry-CD measurements with DewA and ionic liquids were performed on an Applied Photophysics Chirascan Spectrometer at 24°C.…”

Section: Methodsmentioning

confidence: 99%

“…EAS ⌬15 is a truncated version of EAS, a class I hydrophobin from the bread mold Neurospora crassa, which forms amphipathic rodlets on the spore surface (14,15). We have determined previously the three-dimensional structures of the monomeric forms of both EAS and EAS ⌬15 and have demonstrated that the long Cys 3 -Cys 4 loop is not necessary for rodlet formation or stability (14,16).…”

mentioning

confidence: 99%

Recruitment of Class I Hydrophobins to the Air:Water Interface Initiates a Multi-step Process of Functional Amyloid Formation

Morris

Ren

Macindoe

et al. 2011

Journal of Biological Chemistry

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Class I fungal hydrophobins form amphipathic monolayers composed of amyloid rodlets. This is a remarkable case of functional amyloid formation in that a hydrophobic:hydrophilic interface is required to trigger the self-assembly of the proteins. The mechanism of rodlet formation and the role of the interface in this process have not been well understood. Here, we have studied the effect of a range of additives, including ionic liquids, alcohols, and detergents, on rodlet formation by two class I hydrophobins, EAS and DewA. Although the conformation of the hydrophobins in these different solutions is not altered, we observe that the rate of rodlet formation is slowed as the surface tension of the solution is decreased, regardless of the nature of the additive. These results suggest that interface properties are of critical importance for the recruitment, alignment, and structural rearrangement of the amphipathic hydrophobin monomers. This work gives insight into the forces that drive macromolecular assembly of this unique family of proteins and allows us to propose a three-stage model for the interface-driven formation of rodlets.Class I hydrophobins are a family of small amphipathic proteins that are produced by filamentous fungi in a monomeric form but are able to self-assemble into amphipathic monolayers composed of amyloid-like structures known as rodlets (1-3). The polymerization of the hydrophobins occurs on contact with a hydrophobic:hydrophilic interface, such as an air:water boundary or when hydrophobins are secreted from the spores and come into contact with the air. Members of the hydrophobin family are characterized by the presence of four disulfide bonds. The amphipathic nature of hydrophobins drives them to the surface of solutions, where they reduce the surface tension (1).Some of the functional roles of the class I hydrophobins include acting as a surfactant at the air:water boundary to reduce the surface tension, which is a barrier to aerial growth of hyphae, and also to form a robust protein coat on spores. This coating provides a hydrophobic external surface that resists wetting and thus facilitates spore dispersal in air (4 -6). The class I hydrophobin rodlets share many of the structural characteristics of amyloid fibrils; formation of the insoluble, fibrillar rodlets is accompanied by conformational change to an ordered cross-␤-secondary structure form and the polymerized rodlets, but not the monomeric form of the protein, bind to the dye thioflavin T (ThT) 4 (2, 7, 8). However, in contrast to other amyloid fibrils, which can often be solubilized by treatment with denaturants such as guanidine hydrochloride or solvents such as dimethyl sulfoxide (9), treatment with acids such as formic and TFA has been reported to be the only method capable of depolymerizing hydrophobin rodlets and regenerating the monomeric form of the hydrophobin proteins in solution (10,11). This is similar to the curli and tafi fibrils produced by bacteria, which have been shown to be functional amyloid and which also req...

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The Hydrophobin EAS Is Largely Unstructured in Solution and Functions by Forming Amyloid-Like Structures

Cited by 139 publications

References 46 publications

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

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

Fiber-dependent amyloid formation as catalysis of an existing reaction pathway

Recruitment of Class I Hydrophobins to the Air:Water Interface Initiates a Multi-step Process of Functional Amyloid Formation

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