As we show, the inhibitors greatly slow fibrillation of their parent proteins, offering a route to designed chemical interventions, and also supporting the hypothesis that steric zippers are the principal structural element of these fibers
As we show, the inhibitors greatly slow fibrillation of their parent proteins, offering a route to designed chemical interventions, and also supporting the hypothesis that steric zippers are the principal structural element of these fibers. One of the two fiber-like steric zippers that we have chosen as a target for inhibitor design is the hexapeptide 306VQIVYK311 from tau, a protein that forms intracellular amyloid fibers in Alzheimers disease17. a non-natural L-amino acid inhibitor of an amyloid fiber that enhances sexual transmission of HIV. Our results indicate that peptides from structure-based designs can disrupt the fibrillation of full-length proteins, including those like tau that lack fully ordered native structures. The finding that dozens of devastating pathologies, including Alzheimers disease, are associated with amyloid fibers has stimulated research on fiber inhibition. Naxagolide One approach employs the self-associating property of proteins that form fibers to poison fibrillation with short peptide segments6C11. A second approach is based on screening for molecules that can disrupt fiber formation12,13. Here we take a third approach to fiber inhibition: structure-based design of non-natural peptides targeted to block the ends of fibers. With advanced sampling techniques and minimizing an appropriate energy function, we computationally identify novel candidate inhibitors Naxagolide from a vast peptide Naxagolide space that interact favorably with our template structure. This approach has become possible following the determination of several dozen fiber-like atomic structures of segments from amyloid-forming proteins14C16. These structures reveal a common motif termed a steric zipper, in which a pair of -sheets is usually held together by the interdigitation of their side-chains14. Using the steric-zipper structures formed by segments of two pathological proteins as templates, here we design inhibitors that cap fiber ends. As we show, the inhibitors greatly slow fibrillation of their parent proteins, offering a route to designed chemical interventions, and also supporting the hypothesis that steric zippers are the principal structural element of these fibers. One of the two fiber-like steric zippers that we have chosen as a target for inhibitor design is the hexapeptide 306VQIVYK311 from tau, a protein that forms intracellular amyloid fibers in Alzheimers disease17. This segment has been shown to be important for fibrillation of the full-length protein and itself forms fibers with biophysical properties similar to full-length tau fibers15,18,19. Our second template for inhibitor design, identified by the 3D Profile algorithm20,21, is the steric-zipper structure of the peptide segment GGVLVN from the amyloid fiber formed by 248PAP286, a proteolytic fragment of prostatic acid phosphatase (PAP), a protein abundant in semen. 248PAP286 fibers (also termed SEVI, or Semen derived Enhancer of Virus Contamination) enhance HIV contamination by orders of magnitude in cell culture studies, while the monomeric peptide is usually inactive22. Our computational approach to designing non-natural peptides that inhibit fibrillation is usually summarized in Fig. 1 for the VQIVYK segment of tau; the same general strategy is used for the GGVLVN segment of 248PAP286. In both systems, we design a tight interface between the inhibiting peptide and the end of the steric zipper to block additional segments from joining the fiber. By sampling L- or D- amino acids, or commercially available non-natural amino acids, we can design candidate inhibitors with side chains that maximize hydrogen bonding and apolar interactions across FAD the interface. Open in a separate window Physique 1 Scheme for the design and characterization of peptide inhibitors of amyloid fibrillationTau constructs form fibers in vitro (top left)24. The VQIVYK segment in isolation forms fibers and microcrystals (bottom left). The atomic structure of the fiber-like VQIVYK segment reveals a characteristic steric zipper motif15, comprising a pair of interacting -sheets running along the fiber axis (grey arrow), in purple and grey (bottom right). We designed a D-amino acid peptide to bind to the end of the steric zipper template and prevent fiber elongation (middle right). The D-peptide, in red, is designed to satisfy hydrogen bonds and make favorable apolar interactions with the molecule below, while preventing the addition of other molecules above and on the opposite -sheet. As shown (Fig. 4c, Supplementary Figs. 17,18). In the presence of twofold molar excess of this inhibitor, seeded fibrillation is usually efficiently blocked for more than two days (Fig. 4c). Further, we see that increasing the concentration of this inhibitor extends the fibrillation lag time.