Science Concentrates STRUCTURAL BIOLOGY
Surprising amyloid structure solved Bacterial peptide forms amyloids with α-helices instead of β-sheets; new structures could be targets for antibiotics
she realize she was looking at an α-helical version of an amyloid fibril. During their studies, the researchers learned that PSMα3 is most toxic to cells in its fibrillar form. So Landau plans to use the When Meytal Landau, a structural biologist PSMα3 is a major contributor to S. aureus’s newly acquired structure to design inhibiat Technion—Israel Institute of Technology, virulence. tors of the amyloid as potential antibiotics. recently solved the structure of some pepLandau and coworkers expected PSMα3 Inhibiting formation of the PSMα3 amyloid tide fibrils she believed were amyloids, she to be an amyloid because it formed eloncould provide a way to decrease virulence nearly fell out of her chair. She expected to gated, unbranched fibrils that bind the without threatening the bacterium’s life. see the β-sheet architecture that’s common amyloid-indicator dye Thioflavin T. Yet Thus, the bacterium would be less likely to to all identified amyloid fibrils. Instead, she they wrestled to make sense of their X-ray develop antibiotic resistance. saw the first known α-helical The study makes clear that version (Science 2017, DOI: amyloid-like fibrillar struc10.1126/science.aaf4901). tures can be made from differAmyloid fibrils are protein ent secondary structures, says aggregates that pack together Wilfredo Colón, a chemist at to form long strands. Many Rensselaer Polytechnic Instiof these fibrils are involved tute who studies protein agin diseases, such as the amygregation. “One should not be loid-β plaques in Alzheimer’s surprised if a new amyloid-like and the α-synuclein aggrestructure is discovered congates in Parkinson’s. The taining both α and β structures β-sheet structural motif had or with the ability to form both been so ubiquitous among types of fibril.” amyloids that researchers “I never saw this coming,” thought it was required in orBacterial α-helical amyloid-like fibrils (left) are structurally similar says Daniel Otzen, a biophysider for the aggregates to form. to human β-rich amyloid fibrils (right). In both cases, the peptides cist at Aarhus University who But that may not be the case. align perpendicular to the fibril axis. studies protein fibrillation. PSMα3 is the most cy“We can perhaps expect more totoxic member of a family of peptides crystallography data for months. “At first surprises like this as we continue to delve secreted by the bacterium Staphylococcus when I figured out that the structure is into functional amyloids. They are truly aureus. It’s an example of a “functional helical, I was mad that I had spent all this evolutionarily optimized structures, not amyloid,” one that is beneficial rather than time,” Landau says. She thought she had just pathetic failures like pathological harmful to the organism that produces it. solved the wrong form of the peptide—a aggregates, and nature will use whatever Involved in disintegrating human cells, monomer rather than a fibril. Only later did works.”—CELIA ARNAUD
AGRICULTURE
CREDIT: EINAV TAYEB-FLIGELMAN
Slow-release nanofertilizer could boost crop yields Nitrogen fertilizers used to grow crops around the globe have a problem. More than three-quarters of their nutrients get washed away before plants can absorb them, wasting money and creating environmental messes downstream. Now, researchers have developed nanoparticle fertilizers that release nutrients slowly over a week, giving crops more time to take them up (ACS Nano 2017, DOI: 10.1021/ acsnano.6b07781). Conventional slow-release fertilizers consist of urea coated in water-insoluble sulfur or polymers. Such fertilizers reduce
runoff that can lead to harmful algal blooms in waterways, says Gehan Amaratunga of the University of Cambridge. But these fertilizers are expensive and haven’t been shown to increase crop yield. Amaratunga and his colleagues decided to try a new strategy: They attached nitrogen-laden urea molecules to nanoparticles of hydroxyapatite, a naturally occurring form of calcium phosphate. In water, the urea-hydroxyapatite combination released its nitrogen payload over the course of a week, compared with pure urea, which released its nitrogen over a few
minutes. When tested on rice crops in Sri Lanka, the nanofertilizer increased yields by 10%, even though it delivered only half the amount of urea compared with traditional fertilizer. Richard Liu of Ohio State University says the nanocomposite fertilizer looks more promising than other slow-release options for increasing crop yields and reducing costs and environmental risks. He expects that it could be used in most agricultural areas around the globe and on a variety of crops, such as wheat, corn, and soybeans.—
KATHARINE GAMMON, special to C&EN FEBRUARY 27, 2017 | CEN.ACS.ORG | C&EN
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