Play a Flash game and learn about amyloids in your world: from salmonella to the strength of spider silk, from what nanotechnology is to future technology. The Emergent Universe, an online interactive science museum about emergence.
Imagine a transparent window coating that creates electricity, or a plastic chip that powers your MP3 player. Organic solar cells – cheap, lightweight polymer-based materials that convert sunlight to electricity – offer just such promises. But they will only be realized if scientists can increase the conductivity of these materials, enabling the sunlight-generated charges to flow more efficiently to the external circuit. Amyloid fibrils have been shown to align the conducting polymers in such cells, creating nanoscale wires and increased current output.
Tiny nanoscale electronic circuits hold great technological promise for applications ranging from electronic paper to medical implants, because they are smaller, use less energy, and can be embedded in more flexible materials than conventional silicon circuitry can. Scientists have demonstrated that nanoscale wires and transistors can be made from amyloid fibrils by coating them with metals or conducting polymers. Using amyloid fibrils to create nanoscale circuitry is especially appealing, because their tendency to self-assemble could greatly simply the fabrication process.
Tissue
engineering is a relatively new science. Its purpose is to develop
methods for replacing or repairing damaged body tissue, especially
organs and bone. In prototype studies, amyloid fibrils have been used
to provide scaffolding for new tissue growth. Cell receptors are
attached to the amyloid scaffolding to attract the tissue cells. It
is hypothesized that the nanoscale
size of the amyloid fibrils may allow scientists to control the
receptor spacing and thus the receptor-cell interactions.
Some amyloid fibrils form gel-like materials, called hydrogels, which can encapsulate drugs. Often, the proteins that make up these fibrils will only self-aggregate once they’ve folded into a “Beta-turn.” Researchers have designed proteins that only make the Beta-turn under specific conditions, enabling them to turn hydrogel formation and drug encapsulation on and off. Such designed proteins, in which the interactions are chosen to control conditions of amyloid formation, could open doors for targeted drug delivery.
By attaching enzymes -- biological molecules that catalyze reactions -- to amyloid fibrils, and loading these now catalytically active fibrils onto a filter, researchers have created a prototype filter for cleaning polluted water. This prototype filter was found to be active and stable over time. Indeed, due to the nanoscale size of amyloid fibrils, they may provide an ideal support structure for many different types of enzymes, leading to filters with high enzyme density and sustainable catalytic activity.
Our bodies produce antibodies to attack foreign bacteria and viruses, called antigens. Because the antibodies produced bind only to their associated antigen, antibody-antigen binding is used to test for the presence of specific infections, like HIV or mononucleosis. Research shows that antibodies retain their antigen-binding ability when attached to amyloid fibrils. These results suggest that amyloid fibrils could be used as scaffolding for nanoscale-sized infection tests, enabling doctors to test for many infections simultaneously using only small amounts of blood.
Orb weaver spiders, which include many common garden spiders, produce up to 6 different silks for different purposes. Dragline silk, which is used as the spider’s lifeline, as well as for the spokes and outer rim of the web, contains amyloid fibrils. Stronger than steel yet extremely flexible, this amyloid-based spider silk is being considered for many uses, from bullet-proof vests to stitches to scaffolding for in vivo ligament growth.
Green Lacewing larvae are predatory insects often used for pest control in organic gardens. The adult Green Lacewing lays its eggs at the end of an incredibly thin stalk, a tactic that helps to protect the larvae. These stalks are typically thinner than a fine human hair and about a centimeter long; yet they are strong enough to hold the weight of the hatchlings. What are these amazing stalks made of? Why, amyloid fibrils of course!
Many filament-shaped species of green algae live attached to plants, rocks, and other substrates. For such algae to survive, their attachment adhesives must be able to withstand repeated stresses, such as wave action or footsteps. Some of these algae appear to use an amyloid-fibril-based adhesive. The resulting bonds are extremely strong, and they appear to avoid rupture by self-healing after stress, a feature thought to stem from the ability of amyloid fibrils to self-assemble.
Salmonella are disease-causing bacteria commonly found in poultry and meat. They secrete an amyloid-fibril adhesive that helps them stick to surfaces and to each other, and thus to self-aggregate into surface films (also an emergent phenomenon!). Forming films enables Salmonella to colonize in host intestines and to survive on surfaces outside the host. Salmonella surviving on jalapeño and serrano peppers, most likely in films, were responsible for a major outbreak of Salmonellosis in the U.S. in 2008.
The bacteria S. coelicolor is a source of medicinal antibiotics. To reproduce, this moist-soil-dwelling bacteria must shoot a spore stalk out into the air. To help this stalk break free of its wet environment, it excretes proteins that spontaneously aggregate into water-repelling amyloid fibrils at the air-water interface. Thus, when the stalk encounters air, it develops a water-repellant amyloid coating that promotes its escape. The image shows S. coelicolor producing antibiotic (blue color).
In municipal wastewater treatment, bacteria suspended in an “activated sludge” are used to metabolize organic pollutants, converting them into water, carbon dioxide, and more bacteria. Because these bacteria aggregate into particles, called flocs, they are easily separated from the treated water. Recent research suggests that amyloid is a substantial component of the natural extracellular material that helps bind these bacteria into flocs.
Melanin is a pigment in your skin that protects against UV and oxidative damage. Researchers have discovered that melanin production involves amyloid fibrils of the protein Pmel17, providing the first example of a non-disease-associated amyloid in humans. Synthesis of this amyloid occurs rapidly in a specialized compartment, presumably to protect cells from exposure to small clusters of the Pmel17 protein, the potentially toxic amyloid precursor.
The annual killifish A. limnaeus lives in ephemeral ponds in the Venezuelan coastal desert. When the ponds evaporate, the adult killifish die, but their egg embryos can survive the extreme desert conditions until the rains return. These embryos demonstrate an unprecedented resistance to water loss, and amyloid fibrils in the embryo egg casings may be partially responsible. Researchers found that the amount of Beta-sheet structure, and thus presumably of amyloid fibrils, increases in desiccating conditions and decreases again on rehydration.
Eggshells must accomplish numerous functions, protecting the embryo from physical damage, bacteria, dehydration, etc., while still allowing the embryo to breathe. The silk-moth eggshell uses progressively rotating layers of ordered, protein-based fibers to accomplish these tasks. Model protein fragments that closely resemble the proteins in silk-moth eggshells have been shown to spontaneously form amyloid fibrils, strongly suggesting that the fibers that make up silk-moth eggshells are also amyloid.
You have probably heard of nanotechnology – technology based on nanoscale-sized materials. But how small, really, is a nanoscale material? Technically, nanoscale means in the size range of nanometers, where a nanometer is 10-9 meters…uh, right. Ok, think of a meter stick. A decimeter is 1/10 of a meter, written as 10-1 meters. A centimeter is 10 times smaller, or 1/100 of a meter (10-2m). A millimeter is 10 times smaller yet (10-3m), or about the thickness of a dime. Another 10 times smaller (for 10-4m) is the width of a thick human hair. Bacteria are typically about another 100 times smaller (10-6m), and viruses 10 times smaller yet at 10-7m. So at 10-9m nanoscale materials are about 100 times smaller than viruses. An example nanoscale material is DNA. Its diameter is two times 10-9m, or 2 nanometers.
Overview of some amyloid materials research areas: C. Arnold, From diseases to devices, Chem. & Eng. News, 86, 48-50 (July 21, 2008); http://pubs.acs.org/cen/science/86/8629sci1.html
A news item about the potential for designing amyloid materials: Could amyloid deposits have potential as nanomaterials? Science Daily (2008); http://www.sciencedaily.com/releases/2008/05/080528105931.htm
Review of functional amyloids found in biological systems: D. M. Fowler, A. V. Koulov, W. E. Balch, J. W. Kelly, Functional amyloid – from bacteria to humans, Trends in Biochemical Sciences 32, 217-224 (2007); http://www.cell.com/trends/biochemical-sciences/abstract/S0968-0004(07)00059-X
Review of amyloid properties and functional amyloid biomaterials: S. L. Gras, Amyloid fibrils: From disease to design, Aust. J. Chem. 60, 333-342 (2007); http://www.publish.csiro.au/paper/CH06485.htm
Review of protein-based materials, including sections on amyloids, includes both natural functional amyloids and new biotechnologies being explored: C. E. MacPhee, D. N. Woolfson, Engineered and designed peptide-based fibrous biomaterials, Curr. Op. Solid State & Mater. Sci. 8, 141-149 (2004); linkinghub.elsevier.com/retrieve/pii/S1359028604000117
Amyloid AND biomaterials, functional amyloids