Molecular tethering effect of C-terminus of amyloid peptide aβ42

Heterochirality-Mediated Cross-Strand Nested Hydrophobic Interaction Effects Manifested in Surface-Bound Peptide Assembly Structures

Amino acid chirality has been envisioned as an important strategy to regulate structure and function of peptide self-assembled architectures. However, the molecular mechanism of chirality effects in peptide assemblies remains largely elusive. Here, the assembly structures of l-peptide polyphenylalanine F10 (FFFFFFFFFF) and block heterochiral peptide F5f5 (FFFFFfffff) composed of two FFFFF repeat blocks with opposite chirality were characterized at the single-molecule level by using scanning tunneling microscopy. Each peptide formed two distinctively different assembly structures on the HOPG surface, in which peptide chains took parallel and antiparallel β-sheet conformations, respectively. The molecular-level observations revealed that the staggered arrangement of cross-strand side chains achieved in the antiparallel β-sheet structure of the block heterochiral peptide facilitated intimate packing of side chains and maximized inter-residue van der Waals interactions, which led to more residues participating in assembly and greatly stabilized the β-sheet structure of the surface-bound peptide assembly, but such cross-strand nested interactions were not accessible in the heterochiral parallel β-sheet structure and the enantiomerically pure assembly structures. This work could contribute to the molecular insights of stereochemical interactions in peptide assemblies and feasibility of extending this block heterochirality pattern to other peptides with various lengths and amino acid compositions for structural regulations.

Hydrogen Bond Surrogate-Constrained Dynamic Antiparallel β-Sheets

Antiparallel β-sheets are important secondary structures within proteins that equilibrate with random-coil states; however, little is known about the exact dynamics of this process. Here, the first dynamic β-sheet models that mimic this equilibrium have been designed by using an H-bond surrogate that introduces constraint and torque into a tertiary amide bond. 2D NMR data sufficiently reveal the structure, kinetics, and thermodynamics of the folding process, thereby leading the way to similar analysis in isolated biologically relevant β-sheets.

Structural conversion of human islet amyloid polypeptide aggregates under an electric field

Electric fields (EFs) in biological systems are well known, and their presence implies the activity of protein ion channels and pumps in various cells. The aggregation of islet amyloid polypeptides (IAPP) was recently found in human brain tissue, and this was related to the electrical activity of neurons and caused neuronal loss. However, the association between amyloid formation and the electric field is still unknown. Herein a direct method to stimulate the formation of the hIAPP peptide under an EF is reported.

Disassembling and degradation of amyloid protein aggregates based on gold nanoparticle-modified g-C3N4

Amyloid protein misfolds, abnormally aggregates and accumulates into amyloid deposits which endanger tissue functions and are closely related to the pathogenesis of many diseases including Type 2 Diabetes Mellitus (T2DM). There are on-going efforts to find new methods or effective reagents to disassemble and eliminate the existing amyloid aggregates. Herein, we showed that a gold nanoparticle-modified quasi-2D nanomaterial, Au/g-C3N4, could efficiently degrade preformed amyloid aggregates. Furthermore, the scavenger experiment revealed this photodegradation effect was depended on the induced oxygen radicals, particularly hydroxyl radical. The new finding in this work could demonstrate that a gold nanoparticle-modified quasi-2D nanomaterial would have potential applications in the strategy design of the treatment of amyloid related diseases in future.

Patterning Porous Networks through Self-Assembly of Programmed Biomacromolecules

Two-dimensional (2D) porous networks are of great interest for the fabrication of complex organized functional materials for potential applications in nanotechnologies and nanoelectronics. This review aims at providing an overview of bottom-up approaches towards the engineering of 2D porous networks by using biomacromolecules, with a particular focus on nucleic acids and proteins. The first part illustrates how the advancements in DNA nanotechnology allowed for the attainment of complex ordered porous two-dimensional DNA nanostructures, thanks to a biomimetic approach based on DNA molecules self-assembly through specific hydrogen-bond base pairing. The second part focuses the attention on how polypeptides and proteins structural properties could be used to engineer organized networks templating the formation of multifunctional materials. The structural organization of all examples is discussed as revealed by scanning probe microscopy or transmission electron microscopy imaging techniques.

Steric Dependence of Chirality Effect in Surface-Mediated Peptide Assemblies Identified with Scanning Tunneling Microscopy

Amino acid chirality has been recognized as an important driving force in constructing peptide architectures, via interactions such as chirality-induced stereochemical effect. The introduction of site-specific chiral conversion of l- and d-amino acids in peptide sequences could enable the pursuit of the chirality effects in peptide assembly. In this work, we characterized the assemblies of heptapeptides with various side chain moieties and their chiral variants using STM. Specifically, two pairs of amino acids, Gln (Q) and Asn (N), Glu (E) and Asp (D), having one methylene difference in their side chains, are selected to elucidate the steric dependence of amino acid chiral effects on surface-bound peptide assemblies. The observed heptapeptide assembly structures reveal that chirality switching of a single amino acid is able to destabilize the surface-mediated peptide assemblies, and this disturbance effect can be positively correlated with the steric hindrance of amino acid side chains. Furthermore, the strength of the impact due to chiral conversion on heptapeptide assembly structure is noticeably dependent on the mutation sites, indicative of structural heterogeneity of chiral effects. These results could contribute to the molecular insights of chirality-induced stereochemical interactions in peptide assembly.

Self-assembly of photochromic diarylethene-peptide conjugates stabilized by β-sheet formation at the liquid/graphite interface

Two-dimensional (2-D) self-assembly of diarylethene (DAE)-peptide conjugates at the octanoic acid/graphite interface was investigated by scanning tunnelling microscopy (STM). The open-ring isomer of a DAE-peptide conjugate formed a stable 2-D molecular assembly with an antiparallel β-sheet structure. Quantitative analysis of surface coverage depending on concentration revealed a stronger stabilization effect of the oligopeptide than that of the alkyl group with a similar side chain length.

Enhanced Photoresponsive Graphene Oxide-Modified g-C3N4 for Disassembly of Amyloid β Fibrils

Protein misfolding and abnormal self-assembly lead to the aggregates of oligomers, fibrils, or senior amyloid β (Aβ) plaques, which are associated with the pathogenesis of many neurodegenerative diseases. Progressive cerebral accumulation of Aβ protein was widely proposed to explain the cause of Alzheimer's disease, for which one promising direction of the preclinical study is to convert the preformed β-sheet structure of Aβ aggregates into innocent structures. However, the conversion is even harder than the modulation of the amyloidosis process. Herein, a graphene oxide/carbon nitride composite was developed as a good photocatalyst for irreversibly disassembling the Aβ aggregates of Aβ(33-42) under UV. Quartz crystal microbalance, circular dichroism spectrum, atomic force microscopy, fluorescent spectra, and mechanical property analysis were performed to analyze this photodegradation process from different aspects for fully understanding the mechanism, which may provide an important enlightenment for the relevant research in this field and neurodegenerative disease study.

Deformation of stable and toxic hIAPP oligomers by liposomes with distinct nanomechanical features and reduced cytotoxicity

Nanoliposomes can induce hIAPP oligomers to undergo fibrillation with distinct mechanical properties and reduced cytotoxicity.

Peptide Self-Assembly and Its Modulation: Imaging on the Nanoscale

This chapter intends to review the progress in obtaining site-specific structural information for peptide assemblies using scanning tunneling microscopy. The effects on assembly propensity due to mutations and modifications in peptide sequences, small organic molecules and conformational transitions of peptides are identified. The obtained structural insights into the sequence-dependent assembly propensity could inspire rational design of peptide architectures at the molecular level.

Identifying Terminal Assembly Propensity of Amyloidal Peptides by Scanning Tunneling Microscopy

The abnormal accumulation of beta-amyloids (Aβ) in brain is considered as a key initiating cause for Alzheimer's disease (AD) due to their richness in plaques and self-aggregate propensity. In recent studies, N-terminally extended Aβ peptides (NTE-Aβ) with the N-terminus originating prior to the canonical β-secretase cleavage site were found in humans and suggested to have possible relevance to AD. However, the effects of the extended N-terminus on the amyloidegenic structure and aggregation propensity have not been fully elucidated. Herein, we characterized the assembly structures of Aβ1-42, Aβ(-5)-42, Aβ(-10)-42 and Aβ(-15)-42 with both normal and reversed sequences on highly oriented pyrolytic graphite (HOPG) surfaces with scanning tunneling microscopy (STM). The molecularly resolved surface-mediated peptide assemblies enable identification of amyloidegenic fragments. The observations reveal that the assembly propensity of the C-terminal strand of Aβ1-42 is highly conserved and insensitive to N-terminal extensions. In contrast, different assembly structures of the N-terminal strand of Aβ variants can be observed with possible assignment of varied amyloidegenic fragments in the extended N-termini, which may contribute to the varied aggregation propensities of Aβ42 species.

Evaluation of the photo-degradation of Alzheimer's amyloid fibrils with a label-free approach

Degradation of amyloid-β (Aβ) aggregates has been considered as an attractive therapeutic and preventive strategy against Alzheimer's disease (AD). However, an in situ, real-time, and label-free technique is still lacking to understand the degradation process of Aβ aggregates. In this work, we developed a novel method to quantitatively evaluate the degradation of Aβ fibrils by photoactive meso-tetra(4-sulfonatophenyl)porphyrin under UV irradiation with quartz crystal microbalance (QCM).

Supramolecular Assemblies on Surfaces: Nanopatterning, Functionality, and Reactivity

Understanding how molecules interact to form large-scale hierarchical structures on surfaces holds promise for building designer nanoscale constructs with defined chemical and physical properties. Here, we describe early advances in this field and highlight upcoming opportunities and challenges. Both direct intermolecular interactions and those that are mediated by coordinated metal centers or substrates are discussed. These interactions can be additive, but they can also interfere with each other, leading to new assemblies in which electrical potentials vary at distances much larger than those of typical chemical interactions. Earlier spectroscopic and surface measurements have provided partial information on such interfacial effects. In the interim, scanning probe microscopies have assumed defining roles in the field of molecular organization on surfaces, delivering deeper understanding of interactions, structures, and local potentials. Self-assembly is a key strategy to form extended structures on surfaces, advancing nanolithography into the chemical dimension and providing simultaneous control at multiple scales. In parallel, the emergence of graphene and the resulting impetus to explore 2D materials have broadened the field, as surface-confined reactions of molecular building blocks provide access to such materials as 2D polymers and graphene nanoribbons. In this Review, we describe recent advances and point out promising directions that will lead to even greater and more robust capabilities to exploit designer surfaces.

Differential Modulating Effect of MoS2 on Amyloid Peptide Assemblies

The abnormal fibrillogenesis of amyloid peptides such as amyloid fibril and senior amyloid plaques, is associated with the pathogenesis of many amyloid diseases. Hence, modulation of amyloid assemblies is related to the possible pathogenesis of some diseases. Some two-dimensional nanomaterials, that is, graphene oxide, tungsten disulfide, exhibit strong modulation effects on the amyloid fibrillogenesis. Herein, the modulation effect of molybdenum disulfide on two amyloid peptide assemblies based on the label-free techniques is presented, including quartz crystal microbalance (QCM), AFM, and CD spectroscopy. MoS₂ presents different modulating effects on the assembly of amyloid-β peptide (33-42) [Aβ (33-42)] and amylin (20-29), mainly owing to the distinct affinity between amyloid peptides and MoS₂ . This is to our knowledge the first report of MoS₂ as a modulator for amyloid aggregation. It enriches the variety of 2D nanomodulators of amyloid fibrillogenesis and explains the mechanism for the self-assembly of amyloid peptides, and expands the applications of MoS₂ in biology.

Tuning protein assembly pathways through superfast amyloid-like aggregation

Three structural elements for protein assembly are proposed, which guide superfast amyloid-like globular protein aggregation towards macroscopic nanofilms and microparticles.

Biotin–avidin interaction triggers conversion of triskelion peptide nanotori into nanochains

Triskelion biotinylated peptide is self-assembled into nanotorus structures followed by dimerization and chain formation in the presence of avidin.

Dual-affinity peptide mediated inter-protein recognition

We present for the first time an enhanced interaction affinity between an abundant soluble protein (human serum albumin) and a membrane protein (chemokine receptor 4) mediated by a dual-affinity peptide E5.

Copper Ion Binding Site in β-Amyloid Peptide

β-Amyloid aggregates in the brain play critical roles in Alzheimer's disease, a chronic neurodegenerative condition. Amyloid-associated metal ions, particularly zinc and copper ions, have been implicated in disease pathogenesis. Despite the importance of such ions, the binding sites on the β-amyloid peptide remain poorly understood. In this study, we use scanning tunneling microscopy, circular dichroism, and surface-enhanced Raman spectroscopy to probe the interactions between Cu²⁺ ions and a key β-amyloid peptide fragment, consisting of the first 16 amino acids, and define the copper-peptide binding site. We observe that in the presence of Cu²⁺, this peptide fragment forms β-sheets, not seen without the metal ion. By imaging with scanning tunneling microscopy, we are able to identify the binding site, which involves two histidine residues, His13 and His14. We conclude that the binding of copper to these residues creates an interstrand histidine brace, which enables the formation of β-sheets.

Synergistic Inhibitory Effect of Peptide-Organic Coassemblies on Amyloid Aggregation

Inhibition of amyloid aggregation is important for developing potential therapeutic strategies of amyloid-related diseases. Herein, we report that the inhibition effect of a pristine peptide motif (KLVFF) can be significantly improved by introducing a terminal regulatory moiety (terpyridine). The molecular-level observations by using scanning tunneling microscopy reveal stoichiometry-dependent polymorphism of the coassembly structures, which originates from the terminal interactions of peptide with organic modulator moieties and can be attributed to the secondary structures of peptides and conformations of the organic molecules. Furthermore, the polymorphism of the peptide-organic coassemblies is shown to be correlated to distinctively different inhibition effects on amyloid-β 42 (Aβ42) aggregations and cytotoxicity.

The influence of the localised charge of C- and N-termini on peptide self-assembly

The charge of a peptide influences final assembled structures. It is important to consider not only global charge, but also local, such as that found on the terminal residues. This work investigates the change of peptide self-assembly through the selection of different amino acid sequences and by varying the local charge of the residues on the C- and N-termini.

Size Effect of Graphene Oxide on Modulating Amyloid Peptide Assembly

Protein misfolding and abnormal assembly could lead to aggregates such as oligomer, proto-fibril, mature fibril, and senior amyloid plaques, which are associated with the pathogenesis of many amyloid diseases. These irreversible amyloid aggregates typically form in vivo and researchers have been endeavoring to find new modulators to invert the aggregation propensity in vitro, which could increase understanding in the mechanism of the aggregation of amyloid protein and pave the way to potential clinical treatment. Graphene oxide (GO) was shown to be a good modulator, which could strongly control the amyloidosis of Aβ (33-42). In particular, quartz crystal microbalance (QCM), circular dichroism (CD) spectroscopy, and atomic force microscopy (AFM) measurements revealed the size-dependent manner of GO on modulating the assembly of amyloid peptides, which could be a possible way to regulate the self-assembled nanostructure of amyloid peptide in a predictable manner.