Spontaneous self-assembly of SC3 hydrophobins into nanorods in aqueous solution

Hydrophobins are small surface active proteins secreted by filamentous fungi. Because of their ability to self-assemble at hydrophilic-hydrophobic interfaces, hydrophobins play a key role in fungal growth and development. In the present work, the organization in aqueous solution of SC3 hydrophobins from the fungus Schizophyllum commune was assessed using Dynamic Light Scattering, Atomic Force Microscopy and fluorescence spectroscopy. These complementary approaches have demonstrated that SC3 hydrophobins are able not only to spontaneously self-assemble at the air-water interface but also in pure water. AFM experiments evidenced that hydrophobins self-assemble in solution into nanorods. Fluorescence assays with thioflavin T allowed establishing that the mechanism governing SC3 hydrophobin self-assembly into nanorods involves β-sheet stacking. SC3 assembly was shown to be strongly influenced by ionic strength and solution pH. The presence of a very low ionic strength significantly favoured the protein self-assembly but a further increase of ions in solution disrupted the protein assembly. It was assessed that solution pH had a significant effect on the SC3 hydrophobins organization. In peculiar, the self-assembly process was considerably reduced at acidic pH. Our findings demonstrate that the self-assembly of SC3 hydrophobins into nanorods of well-defined length can be directly controlled in solution. Such control allows opening the way for the development of new smart self-assembled structures for targeted applications.     

Hierarchical ionic self-assembly of rod-comb block copolypeptide-surfactant complexes

Novel hierarchical nanostructures based on ionically self-assembled complexes of diblock copolypeptides and surfactants are presented. Rod-coil diblock copolypeptide poly(gamma-benzyl-L-glutamate)-block-poly(L-lysine), PBLG-b-PLL (Mn = 25,000 and 8000 for PBLG and PLL, respectively, polydispersity index 1.08), was complexed with anionic surfactants dodecanesulfonic acid (DSA) or dodecyl benzenesulfonic acid (DBSA), denoted as PBLG-b-PLL(DSA)1.0 and PBLG-b-PLL(DBSA)1.0, respectively. The complexation leading to supramolecular rod-comb architectures was studied by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR), and polarized optical microscopy (POM). PBLG-b-PLL, PBLG-b-PLL(DBSA)1.0, and PBLG-b-PLL(DSA)1.0 self-assemble with alternating PBLG lamellae and PLL-containing lamellae with a periodicity of 27-33 nm. Within the PBLG lamellae, the rod-like PBLG helices pack with a periodicity of ca. 1.3 nm. The internal structure of the PLL-containing lamellae depends on the complexation. For pure PBLG-b-PLL, the PLL chains adopt a random coil conformation and the PLL domains are disordered. For PBLG-b-PLL(DSA)1.0, lamellar self-assembly of periodicity of 3.7 nm within the PLL(DSA)1.0 domains is observed due to crystalline packing of the linear n-dodecyl tails. For PBLG-b-PLL(DBSA)1.0 with branched dodecyl tails, a distinct SAXS reflection is observed, suggesting self-assembly within the PLL(DBSA)1.0 domains with a periodicity of 2.9 nm. However, due to the absence of higher order reflections, the internal structure cannot be conclusively assigned. The efficient plasticization which leads to fluid-like liquid crystallinity in PBLG-b-PLL(DBSA)1.0 and an alpha-helical conformation according to FTIR allows us to suggest that the PLL(DBSA)1.0 domains have a hexagonal internal structure. The interplay of self-assembly at different length scales combined with rod-like liquid crystallinity can open new routes to design functional materials.     

Annulate lamellae,lamellar bodies and subsurface cisternae in neurons of the avian hyperstriatum accessorium

Summary Structures identified as annulate lamellae, lamellar bodies and subsurface cisternae were found in neurons of the hyperstriatum accessorium of the avian forebrain. Annulate lamellar arrays with up to six lamellae were present in the larger somata. The lamellae were made up of fused smooth-surfaced cisternae forming pores or annuli and were surrounded by a dense filamentous to granular material. Stacks of nonfenestrated, parallel, regularly spaced cisternae, designated as lamellar bodies, also appeared in the cytoplasm. When flattened they were reminiscent of the electron dense subsurface cisternae. Continuity could be demonstrated between peripherally located subsurface cisternae and lamellar bodies. The dense filamentous to finely granular substance was also located between these structures. Annulate lamellae, lamellar bodies and subsurface cisternae were always observed in conjunction with the rough endoplasmic reticulum. The functional significance of these structural associations is considered.     

Hydrophobins, from molecular structure to multiple functions in fungal development

Mycelial fungi secrete small, cysteine-rich, proteins, called hydrophobins, that self-assemble at hydrophilic-hydrophobic interfaces into amphipathic membranes, highly insoluble in case of Class I hydrophobins. By self-assembly at the culture medium-air interface they greatly lower the surface tension enabling emergent structures to grow into the air. By self-assembly at the interface between the hydrophilic cell wall and the air or any other hydrophobic environment, these emergent structures are coated with a hydrophobin membrane. These properties allow hydrophobins to fulfil a broad spectrum of functions in fungal development. They are involved in formation of aerial (reproductive) structures, in aerial dispersion of spores, and they line air channels within fruiting bodies with a hydrophobic coating, probably serving gas exchange. Hydrophobins also mediate hyphal attachment to hydrophobic surfaces such as those of plants. Moreover, they appear involved in complex interhyphal interactions, and in interactions with algae in lichens. Their resistance towards chemical and enzymatic treatments suggests that assembled hydrophobins also protect fungal emergent structures against adverse environmental conditions.     

Compactness Determines the Success of Cube and Octahedron Self-Assembly

Nature utilizes self-assembly to fabricate structures on length scales ranging from the atomic to the macro scale. Self-assembly has emerged as a paradigm in engineering that enables the highly parallel fabrication of complex, and often three-dimensional, structures from basic building blocks. Although there have been several demonstrations of this self-assembly fabrication process, rules that govern a priori design, yield and defect tolerance remain unknown. In this paper, we have designed the first model experimental system for systematically analyzing the influence of geometry on the self-assembly of 200 and 500 µm cubes and octahedra from tethered, multi-component, two-dimensional (2D) nets. We examined the self-assembly of all eleven 2D nets that can fold into cubes and octahedra, and we observed striking correlations between the compactness of the nets and the success of the assembly. Two measures of compactness were used for the nets: the number of vertex or topological connections and the radius of gyration. The success of the self-assembly process was determined by measuring the yield and classifying the defects. Our observation of increased self-assembly success with decreased radius of gyration and increased topological connectivity resembles theoretical models that describe the role of compactness in protein folding. Because of the differences in size and scale between our system and the protein folding system, we postulate that this hypothesis may be more universal to self-assembling systems in general. Apart from being intellectually intriguing, the findings could enable the assembly of more complicated polyhedral structures (e.g. dodecahedra) by allowing a priori selection of a net that might self-assemble with high yields.     

Structural and functional role of the disulfide bridges in the hydrophobin SC3

Hydrophobins function in fungal development by self-assembly at hydrophobic-hydrophilic interfaces such as the interface between the fungal cell wall and the air or a hydrophobic solid. These proteins contain eight conserved cysteine residues that form four disulfide bonds. To study the effect of the disulfide bridges on the self-assembly, the disulfides of the SC3 hydrophobin were reduced with 1,4-dithiothreitol. The free thiols were then blocked with either iodoacetic acid (IAA) or iodoacetamide (IAM), introducing eight or zero negative charges, respectively. Circular dichroism and infrared spectroscopy showed that after opening of the disulfide bridges SC3 is initially unfolded. IAA-SC3 did not self-assemble at the air-water interface upon shaking an aqueous solution. Remarkably, after drying down IAA-SC3 or after exposing it to Teflon, it refolded into a structure similar to that observed for native SC3 at these interfaces. Iodoacetamide-SC3 on the other hand, which does not contain extra charges, spontaneously refolded in water in the amyloid-like beta-sheet conformation, characteristic for SC3 assembled at the water-air interface. From this we conclude that the disulfide bridges of SC3 are not directly involved in self-assembly but keep hydrophobin monomers soluble in the fungal cell or its aqueous environment, preventing premature self-assembly.     

Self-aggregation characteristics of recombinantly expressed human elastin polypeptides.

Elastin is an extracellular matrix protein found in tissues requiring extensibility and elastic recoil. Monomeric elastin has the ability to aggregate into fibrillar structures in vitro, and has been suggested to participate in the organization of its own assembly into a polymeric matrix in vivo. Although hydrophobic sequences in elastin have been suggested to be involved in this process of self-organization, the contributions of specific hydrophobic and crosslinking domains to the propensity of elastin to self-assemble have received less attention. We have used a series of defined, recombinant human elastin polypeptides to investigate the factors contributing to elastin self-assembly. In general, coacervation temperature of these polypeptides, used as a measure of their propensity to self-assemble, was influenced both by salt concentration and polypeptide concentration. In addition, hydrophobic domains appeared to be essential for the ability of these polypeptides to self-assemble. However, neither overall molecular mass, number of hydrophobic domains nor general hydropathy of the polypeptides provided a complete explanation for differences in coacervation temperature, suggesting that the specific nature of the sequences of these hydrophobic domains are an important determinant of the ability of elastin polypeptides to self-assemble.     

Self-assembly of proteins into a three-dimensional multilayer system: Investigation of the surface of the human fungal pathogen Aspergillus fumigatus

Hydrophobins are small surface active proteins that fulfil a wide spectrum of functions in fungal growth and development. The human fungal pathogen Aspergillus fumigatus expresses RodA hydrophobins that self-assemble on the outer conidial surface into tightly organized nanorods known as rodlets. AFM investigation of the conidial surface allows us to evidence that RodA hydrophobins self-assemble into rodlets through bilayers. Within bilayers, hydrophilic domains of hydrophobins point inward, thus making a hydrophilic core, while hydrophobic domains point outward. AFM measurements reveal that several rodlet bilayers are present on the conidial surface thus showing that proteins self-assemble into a complex three-dimensional multilayer system. The self-assembly of RodA hydrophobins into rodlets results from attractive interactions between stacked β-sheets, which conduct to a final linear cross-β spine structure. A Monte Carlo simulation shows that anisotropic interactions are the main driving forces leading the hydrophobins to self-assemble into parallel rodlets, which are further structured in nanodomains. Taken together, these findings allow us to propose a mechanism, which conducts RodA hydrophobins to a highly ordered rodlet structure. The mechanism of hydrophobin assembly into rodlets offers new prospects for the development of more efficient strategies leading to disruption of rodlet formation allowing a rapid detection of the fungus by the immune system.     

Gill morphometrics in relation to gas transfer and ram ventilation in high‐energy demand teleosts: Scombrids and billfishes

This comparative study of the gill morphometrics in scombrids (tunas, bonitos, and mackerels) and billfishes (marlins, swordfish) examines features of gill design related to high rates of gas transfer and the high‐pressure branchial flow associated with fast, continuous swimming. Tunas have the largest relative gill surface areas of any fish group, and although the gill areas of non‐tuna scombrids and billfishes are smaller than those of tunas, they are also disproportionally larger than those of most other teleosts. The morphometric features contributing to the large gill surface areas of these high‐energy demand teleosts include: 1) a relative increase in the number and length of gill filaments that have, 2) a high lamellar frequency (i.e., the number of lamellae per length of filament), and 3) lamellae that are long and low in profile (height), which allows a greater number of filaments to be tightly packed into the branchial cavity. Augmentation of gill area through these morphometric changes represents a departure from the general mechanism of area enhancement utilized by most teleosts, which lengthen filaments and increase the size of the lamellae. The gill design of scombrids and billfishes reflects the combined requirements for ram ventilation and elevated energetic demands. The high lamellar frequencies and long lamellae increase branchial resistance to water flow which slows and streamlines the ram ventilatory stream. In general, scombrid and billfish gill surface areas correlate with metabolic requirements and this character may serve to predict the energetic demands of fish species for which direct measurement is not possible. The branching of the gill filaments documented for the swordfish in this study appears to increase its gill surface area above that of other billfishes and may allow it to penetrate oxygen‐poor waters at depth. J. Morphol. 2010. © 2009 Wiley‐Liss, Inc.     

A morphological study on posterior gills of the mangrove crab Ucides cordatus

Morphological and histological studies on posterior gills of the mangrove crab Ucides cordatus showed that the 5th gill (of 7) has a larger surface area and a greater number of lamellae compared to the 6th gill. Regular separation of gill lamellae, important when the gill is in air, is maintained by enlargements of the marginal canals. Conical, spine-like structures along the efferent vessel of both 5th and 6th gills were also observed. In addition, pillar cells, a discontinuous lamellar septum and a hypobranchial artery were observed. The presence of valve-like structures near the efferent vessel was also indicated. These structures, together with the pillar cells, may have a role in directing the hemolymph flow towards certain gills during particular physiological states. Localization of osmoregulatory epithelia in the lamellae of both gills was inferred from dimethylaminostyrylethylpyridiniumiodine staining. Apparently gills 5 and 6 have osmoregulatory epithelial cell patches of similar area, corresponding to 43% and 38% of the total lamellae area, respectively. However, their localization is quite different. Gill number 5 osmoregulatory patches seem to be restricted to the afferent region of the lamella whereas in gill number 6, they are more dispersed over the entire lamella. These differences may be related to the particular functional characteristics of these gills.     

Concentrically arranged endoplasmic reticulum containing some lamellae (bar-like structure) in alveolar type II cells of rat lung

We examined in vivo the effect of pilocarpine (a cholinergic agent) and cycloheximide (an inhibitor of protein synthesis) on the "bar-like structures" in alveolar type II cells of rat lung to clarify their origin and significance in pulmonary surfactant production and secretion. Lungs were examined with an electron microscope using ultrathin sectioning, freeze-fracture technique, and morphometry. The bar-like structures in type II cells consisted of a concentrically arranged endoplasmic reticulum containing some amount of osmiophilic periodic material similar to the lamellae of lamellar bodies. Pilocarpine induced the accumulation of lamellar bodies of normal size which paralleled the increase in the number of bar-like structures in the cytoplasm of the type II cells. Cycloheximide induced a decrease in size of the lamellar bodies and an enlargement of the bar-like structures. Our morphological findings suggest that: The phospholipid that would normally be incorporated into the lamellar bodies might be sequestered instead in the concentrically arranged endoplasmic reticulum, forming the bar-like structures, and The enlargement and the increased number of bar-like structures may be responsible in part for the changed metabolic process of surfactant production by alveolar type II cells.     

Lamellar organization of pigments in chlorosomes, the light harvesting complexes of green photosynthetic bacteria

Chlorosomes of green photosynthetic bacteria constitute the most efficient light harvesting complexes found in nature. In addition, the chlorosome is the only known photosynthetic system where the majority of pigments (BChl) is not organized in pigment-protein complexes but instead is assembled into aggregates. Because of the unusual organization, the chlorosome structure has not been resolved and only models, in which BChl pigments were organized into large rods, were proposed on the basis of freeze-fracture electron microscopy and spectroscopic constraints. We have obtained the first high-resolution images of chlorosomes from the green sulfur bacterium Chlorobium tepidum by cryoelectron microscopy. Cryoelectron microscopy images revealed dense striations approximately 20 A apart. X-ray scattering from chlorosomes exhibited a feature with the same approximately 20 A spacing. No evidence for the rod models was obtained. The observed spacing and tilt-series cryoelectron microscopy projections are compatible with a lamellar model, in which BChl molecules aggregate into semicrystalline lateral arrays. The diffraction data further indicate that arrays are built from BChl dimers. The arrays form undulating lamellae, which, in turn, are held together by interdigitated esterifying alcohol tails, carotenoids, and lipids. The lamellar model is consistent with earlier spectroscopic data and provides insight into chlorosome self-assembly.     

Electron Microscopy of Monkey Kidney Cell Cultures Infected with Rubella Virus

Two rubella virus strains isolated in this laboratory were investigated in terms of their growth in LLC-MK(2) cell cultures and their effect on cell morphology. Rubella virus grew readily in LLC-MK(2) cells, but cytopathic effects of the virus were not observed in infected cultures. Such infected cultures can be subcultured indefinitely and continue to shed virus. Examination of rubella-infected cell cultures by electron microscopy showed the presence of annulate lamellae in the cytoplasm of 15% of the cells. No changes were evident in the nuclei. These membranous inclusions varied in complexity from parallel arrays of annulate lamellae to large lamellar structures of complex morphology. An occasional cell contained a crystal lattice structure in association with the lamellae. Larger inclusions, consisting of disorganized arrays of "unit" membranes, were also found. Uninfected cells were devoid of annulate lamellae, crystals, and complex membranous inclusions. No viruslike particles were observed in any part of the cells from infected cultures. The significance of the structures observed has not been determined.     

Modelling the stratum corneum lipid organisation with synthetic lipid mixtures: the importance of synthetic ceramide composition

Cholesterol (CHOL), free fatty acids (FFA) and nine classes of ceramides (CER1-CER9) form the main constituents of the intercellular lipid lamellae in stratum corneum (SC), which regulate the skin barrier function. Both the presence of a unique 13-nm lamellar phase, of which the formation depends on the presence of CER1, and its dense lateral packing are characteristic for the SC lipid organisation. The present study focuses on the lipid organisation in mixtures prepared with CHOL, FFA and a limited number of synthetic CER, namely CER1, CER3 and bovine brain CER type IV (SigmaCERIV). The main objective is to determine the optimal molar ratio of CER3 to SigmaCERIV for the formation of the 13-nm lamellar phase. CER3 contains a uniform acyl chain length, whereas SigmaCERIV contains fatty acids with varying chain lengths. Using small angle X-ray diffraction (SAXD), it is demonstrated that the CER3 to SigmaCERIV ratio affects the formation of the 13-nm lamellar phase and that the optimal ratio depends on the presence of FFA. Furthermore, the formation of the 13-nm lamellar phase is not very sensitive to variations in the total CER level, which is similar to the in vivo situation.     

Temperature and compositional dependence of the structure of hydrated dimyristoyl lecithin.

Differential scanning calorimetry and x-ray diffraction techniques have been used to investigate the structure and phase behavior of hydrated dimyristoyl lecithin (DML) in the hydration range 7.5 to 60 weight % water and the temperature range -10 to +60 degrees C. Four different calorimetric transitions have been observed: T1, a low enthalpy transition (deltaH approximately equal to 1 kcal/mol of DML) at 0 degrees C between lamellar phases (L leads to Lbeta); T2, the low enthalpy "pretransition" at water contents greater than 20 weight % corresponding to the transition Lbeta leads to Pbeta; T3, the hydrocarbon chain order-disorder transition (deltaH = 6 to 7 kcal/mol of DML) representing the transition of the more ordered low temperature phases (Lbeta, Pbeta, or crystal C, depending on the water content) to the lamellar Lalpha phase; T4, a transition occurring at 25--27 degrees C at low water contents representing the transition from the lamellar Lbeta phase to a hydrated crystalline phase C. The structures of the Lbeta, Pbeta, C, and Lalpha phases have been examined as a function of temperature and water content. The Lbeta structure has a lamellar bilayer organization with the hydrocarbon chains fully extended and tilted with respect to the normal to the bilayer plane, but packed in a distorted quasihexagonal lattice. The Pbeta structure consists of lipid bilayer lamellae distorted by a periodic "ripple" in the plane of the lamellae; the hydrocarbon chains are tilted but appear to be packed in a regular hexagonal lattice. The diffraction pattern from the crystalline phase C indexes according to an orthorhombic cell with a = 53.8 A, b = 9.33 A, c = 8.82 A. In the lamellae bilayer Lalpha strucure, the hydrocarbon chains adopt a liquid-like conformation. Analysis of the hydration characteristics and bilayer parameters (lipid thickness, surface area/molecule) of synthetic lecithins permits an evaluation of the generalized hydration and structural behavior of this class of lipids.     

A lipid-phase separation model of low-temperature damage to biological membranes

An hypothesis is proposed to explain the damage caused to biological membranes exposed to low temperatures. The thesis rests on the general observation that the lipid components of most membranes are heterogeneous and undergo phase transitions from gel-phase lamellae to liquid-crystalline lamellae and some to a non-lamellar, hexagonal-II phase over a wide range of temperatures. As a consequence of these phase transitions the lateral distribution of the lipids characteristic of the growth temperature is disturbed and redistribution takes place on the basis of the temperature at which phase transitions occur. When membranes are cooled, first the non-lamellar forming lipids pass through a transition to a fluid lamellar phase and are miscible with bilayer-forming lipids into which they diffuse. On further cooling the high-melting-point lipids begin to crystallize and separate into a lamellar gel phase, in the process excluding the low-melting point lipids and intrinsic proteins. The lipids in these remaining regions form a gel phase at the lowest temperature. It is suggested that, because the non-lamellar lipids tend to undergo a liquid-crystalline to gel-phase transition at higher temperatures than lamellar-forming lipids, these will tend to phase separate into a gel phase domain rich in these lipids. Damage results when the membrane is reheated, whereupon the hexagonal-II-forming lipids give rise to non-lamellar structures. These probably take the form of inverted micelles sandwiched within the lipid bilayer and they completely destroy the permeability barrier properties of the membrane. The model is consistent with the phase behavior of membrane lipids and the action of cryoprotective agents in modifying lipid phase properties.     

Complexes of annulate lamellae and nemaline bodies in soleplate nuclei in skeletal muscle fibers of the normal rat

Pseudointranuclear inclusions resulting from invaginations of the nuclear envelope, characteristic of myopathic muscles, were found in the soleplate nuclei of normal soleus muscles of rats. Such inclusions had annulate lamellae (AL), nemaline or rod bodies, lamellar structures, a concentric system of membranes, as well as tightly packed sarcoplasmic organelles. An accumulative origin of such included structures was suggested. The AL were sometimes connected directly to the outer membrane enclosing the inclusions, dilated into cisterns and positioned perpendicularly against the nuclear surface. AL, some of which were well-developed, were observed in the same loci as above during the course of denervation atrophy.     

Coarse-grained molecular simulation of self-assembly nanostructures of CTAB on nanoscale graphene

Coarse-grained molecular dynamics simulation has been performed to study the aggregated morphology of the cationic surfactant, cetyltrimethylammonium bromide (CTAB), adsorbed on nanoscale graphene surfaces. The CTAB surfactants can self-assemble on graphene to form various supramolecular morphologies and structures. The effect of packing density, thickness of graphene sheet and width of graphene nanoribbon on the CTAB–graphene self-assembly has been investigated. The buoyant densities of various graphene–CTAB assemblies were calculated, which increase with surfactant coverage and number of graphene layers. This result demonstrates that density gradient can be used to isolate graphenes with various layers. This simulation provides larger-scale microscopic insight into the supramolecular self-assembly nanostructures for the CTAB surfactants aggregated on graphene, which could be valuable to guide fabrication of graphene-based hybrid nanocomposites.     

Modelling the stratum corneum lipid organisation with synthetic lipid mixtures: the importance of synthetic ceramide composition

Cholesterol (CHOL), free fatty acids (FFA) and nine classes of ceramides (CER1-CER9) form the main constituents of the intercellular lipid lamellae in stratum corneum (SC), which regulate the skin barrier function. Both the presence of a unique 13-nm lamellar phase, of which the formation depends on the presence of CER1, and its dense lateral packing are characteristic for the SC lipid organisation. The present study focuses on the lipid organisation in mixtures prepared with CHOL, FFA and a limited number of synthetic CER, namely CER1, CER3 and bovine brain CER type IV (∑CERIV). The main objective is to determine the optimal molar ratio of CER3 to ∑CERIV for the formation of the 13-nm lamellar phase. CER3 contains a uniform acyl chain length, whereas ∑CERIV contains fatty acids with varying chain lengths. Using small angle X-ray diffraction (SAXD), it is demonstrated that the CER3 to ∑CERIV ratio affects the formation of the 13-nm lamellar phase and that the optimal ratio depends on the presence of FFA. Furthermore, the formation of the 13-nm lamellar phase is not very sensitive to variations in the total CER level, which is similar to the in vivo situation.     

Spectroscopic evidence for amyloid-like interfacial self-assembly of hydrophobin Sc3

Amphipathic fungal proteins called hydrophobins are able to self-assemble into insoluble supramolecular structures at hydrophobic/hydrophilic interfaces, but the molecular mechanism and underlying protein conformation changes are not known. Secondary-structure prediction indicated that hydrophobin Sc3 is an all-beta protein. Many amyloidogenic proteins self-assemble into insoluble amyloid fibrils while undergoing a change to an all-beta conformation. In this study we show that two dyes, thioflavin T, and Congo red, which are widely used for specific detection of stacked beta sheets, interact with Sc3 assemblies in the same way as with the amyloid beta-sheet fibrils. We conclude that Sc3, and probably other hydrophobins too, self-assemble at interfaces in the same manner as amyloidogenic proteins, i.e., through beta-sheet stacking.