Significance: Many proteins enter the amyloid state, which is associated with human diseases and is also involved in many biological events. Amyloid formed by various proteins has a uniform “cross-β” structure with protein units stacking repetitively into fibrils. This unique structure brings amyloid favorable mechanical and chemical properties, and inspires the exploration of amyloid as a novel class of bionanomaterials. On the other hand, the uniform fibrillar structure limits the application of amyloid materials for a diverse function. This paper illustrates our discovery, structure characterization, design, and application of an amyloid-based structure, termed “amyloid-like nanosheet.” This nanosheet enriches the architectures of amyloid materials and will aid researchers in designing and investigating amyloid with new functions.

Investigation into the interactions between graphene oxide (GO) and biomolecules is very important for broad applications of GO in bioassay and bioanalysis. In this work, we describe the interactions between double-stranded DNA (dsDNA) and GO. We demonstrated that dsDNA can bind to GO forming complexes (dsDNA/GO) in the presence of certain salts, which protects dsDNA from being enzymatically digested. On the other hand, we found that a nonionic surfactant, such as triton X-100, can block the formation of dsDNA/GO complexes, so that the enzymatic digestion of dsDNA is restored. These results lead us to believe that the reason for GO protecting dsDNA from enzymatic digestion is the formation of dsDNA/GO complexes hindering the access of DNA enzymes to dsDNA, rather than direct inactivation of the DNA enzymes.

Antimicrobial peptides (AMPs) as biocides are of great interest because they have the ability to combat antibiotic resistance. Normally, natural AMPs need to be rationally designed or modified for practical use as an antibiotic. Here, a novel AMP, termed FF8, which is a cationic octapeptide composed of arginine, lysine, and phenylalanine, was designed. The FF8 was found to self-assemble into nanofibers when induced by a negatively charged lipid membrane or pH is above 9.4. The fibers on the membrane broke the lipid membrane, forming pores and significantly reducing its fluidity. FF8 also exhibited enhanced antibacterial activity by significantly increasing the permeability of the inner and outer membranes of Escherichia coli (E. coli) and maintaining the pores of the inner membrane of cells, which caused continuous membrane leakage. Because of its high antibacterial activity, cytocompatibility, and cost-effectiveness, FF8 is a promising antibacterial material.

Tyrosinase is a key enzyme involved in melanin synthesis. Therefore, various tyrosinase inhibitors have been screened by researchers in recent years. In the present study, we discovered a novel tyrosinase inhibitor, a peptide ECGYF (named EF-5), with free radical scavenging ability. The effect of tyrosinase inhibition by EF-5 was stronger than that of arbutin and glutathione, when analyzed both in vitro (IC50: 0.46 mM) and in vivo. The UV-Vis absorption and circular dichroism spectroscopies indicated that EF-5 interacted with tyrosinase in a different way as that of glutathione. The results of molecular docking showed that the binding between EF-5 and tyrosinase was determined majorly by hydrogen bonds and hydrophobic interactions. EF-5 had also retained its ability to scavenge both hydroxyl and superoxide radicals in vitro and was found to be nontoxic to cells, as revealed by the MTT assay. These features suggested that the EF-5 peptide may serve as a safe and effective alternative as a tyrosinase inhibitor.

Surface-assisted self-assembly of amyloid-like peptides has received considerable interest in both amyloidosis research and nanotechnology in recent years. Despite extensive studies, some controlling factors, such as salts, are still not well understood, even though it is known that some salts can promote peptide self-assemblies through the so-called “salting-out” effect. However, they are usually noncontrollable, disordered, amorphous aggregates. Here, we show via a combined experimental and theoretical approach that a conserved consensus peptide NH ₂ -VGGAVVAGV-CONH ₂ (GAV-9) (from representative amyloidogenic proteins) can self-assemble into highly ordered, multilayered nanofilaments, with surprising all-upright conformations, under high-salt concentrations. Our atomic force microscopy images also demonstrate that the vertical stacking of multiple layers is highly controllable by tuning the ionic strength, such as from 0 mM (monolayer) to 100 mM (mainly double layer), and to 250 mM MgCl ₂ (double, triple, quadruple, and quintuple layers). Our atomistic molecular dynamics simulations then reveal that these individual layers have very different internal nanostructures, with parallel β-sheets in the first monolayer but antiparallel β-sheets in the subsequent upper layers due to their different microenvironment. Further studies show that the growth of multilayered, all-upright nanostructures is a common phenomenon for GAV-9 at the mica/water interface, under a variety of salt types and a wide range of salt concentrations.