α-Methylation Enables the X-ray Crystallographic Observation of Oligomeric Assemblies Formed by a β-Hairpin Peptide Derived from Aβ.

The assembly of the β-amyloid peptide Aβ into toxic oligomers plays a significant role in the neurodegeneration associated with the pathogenesis of Alzheimer's disease. Our laboratory has developed -methylation as a tool to enable X-ray crystallographic studies of oligomers formed by macrocyclic β-hairpin peptides derived from Aβ. In this investigation, we set out to determine whether α-methylation could be used as an alternative to -methylation in studying the oligomerization of a β-hairpin peptide derived from Aβ.

Investigation of Isobactin Analogues of Teixobactin.

Although teixobactin is a promising antibiotic drug candidate against Gram-positive bacteria, it aggregates to form gels that may limit intravenous administration. We previously reported -acyl isopeptide prodrugs of teixobactin analogues that address the problem of gel formation while retaining antibiotic activity. We termed these compounds .

A turn for the worse: Aβ β-hairpins in Alzheimer's disease.

Amyloid-β (Aβ) oligomers are a cause of neurodegeneration in Alzheimer's disease (AD). These soluble aggregates of the Aβ peptide have proven difficult to study due to their inherent metastability and heterogeneity. Strategies to isolate and stabilize homogenous Aβ oligomer populations have emerged such as mutations, covalent cross-linking, and protein fusions.

Supramolecular Interactions of Teixobactin Analogues in the Crystal State.

This Note presents the X-ray crystallographic structure of the -methylated teixobactin analogue -Me-d-Gln,Lys-teixobactin (). Eight peptide molecules comprise the asymmetric unit, with each peptide molecule binding a chloride anion through hydrogen bonding with the amide NH group of residues 7, 8, 10, and 11. The peptide molecules form hydrogen-bonded antiparallel β-sheet dimers in the crystal lattice, with residues 1-3 comprising the dimerization interface.

Antibodies Raised Against an Aβ Oligomer Mimic Recognize Pathological Features in Alzheimer's Disease and Associated Amyloid-Disease Brain Tissue.

Antibodies that target the β-amyloid peptide (Aβ) and its associated assemblies are important tools in Alzheimer's disease research and have emerged as promising Alzheimer's disease therapies. This paper reports the creation and characterization of a triangular Aβ trimer mimic composed of Aβ β-hairpins and the generation and study of polyclonal antibodies raised against the Aβ trimer mimic. The Aβ trimer mimic is covalently stabilized by three disulfide bonds at the corners of the triangular trimer to create a homogeneous oligomer.

Amyloid-α Peptide Formed through Alternative Processing of the Amyloid Precursor Protein Attenuates Alzheimer's Amyloid-β Toxicity via Cross-Chaperoning.

Amyloid aggregation is a key feature of Alzheimer's disease (AD) and a primary target for past and present therapeutic efforts. Recent research is making it increasingly clear that the heterogeneity of amyloid deposits, extending past the commonly targeted amyloid-β (Aβ), must be considered for successful therapy. We recently demonstrated that amyloid-α (Aα or p3), a C-terminal peptidic fragment of Aβ, aggregates rapidly to form amyloids and can expedite the aggregation of Aβ through seeding.

β-Hairpin Alignment Alters Oligomer Formation in Aβ-Derived Peptides.

Amyloid-β (Aβ) forms heterogeneous oligomers, which are implicated in the pathogenesis of Alzheimer's disease (AD). Many Aβ oligomers consist of β-hairpin building blocks─Aβ peptides in β-hairpin conformations. β-Hairpins of Aβ can adopt a variety of alignments, but the role that β-hairpin alignment plays in the formation and heterogeneity of Aβ oligomers is poorly understood.

A β-barrel-like tetramer formed by a β-hairpin derived from Aβ.

β-Hairpins formed by the β-amyloid peptide Aβ are building blocks of Aβ oligomers. Three different alignments of β-hairpins have been observed in the structures of Aβ oligomers or fibrils. Differences in β-hairpin alignment likely contribute to the heterogeneity of Aβ oligomers and thus impede their study at high-resolution.

Probing differences among Aβ oligomers with two triangular trimers derived from Aβ.

The assembly of the β-amyloid peptide (Aβ) to form oligomers and fibrils is closely associated with the pathogenesis and progression of Alzheimer's disease. Aβ is a shape-shifting peptide capable of adopting many conformations and folds within the multitude of oligomers and fibrils the peptide forms. These properties have precluded detailed structural elucidation and biological characterization of homogeneous, well-defined Aβ oligomers.

Current Peptide Vaccine and Immunotherapy Approaches Against Alzheimer's Disease.

Peptide vaccines and immunotherapies against aggregating proteins involved in the pathogenesis and progression of Alzheimer's disease (AD) - the β-amyloid peptide (Aβ) and tau - are promising therapeutic avenues against AD. Two decades of effort has led to the controversial FDA approval of the monoclonal antibody Aducanumab (Aduhelm), which has subsequentially sparked the revival and expedited review of promising monoclonal antibody immunotherapies that target Aβ. In this review, we explore the development of Aβ and tau peptide vaccines and immunotherapies with monoclonal antibodies in clinical trials against AD.

Synthesis and Stereochemical Determination of the Peptide Antibiotic Novo29.

This paper describes the synthesis and stereochemical determination of Novo29 (clovibactin), a new peptide antibiotic that is related to teixobactin and is active against Gram-positive bacteria. Novo29 is an eight-residue depsipeptide that contains the noncanonical amino acid hydroxyasparagine of hitherto undetermined stereochemistry in a macrolactone ring. The amino acid building blocks Fmoc-(2,3)-hydroxyasparagine-OH and Fmoc-(2,3)-hydroxyasparagine-OH were synthesized from (,)- and (,)-diethyl tartrate.

Isobactins: -acyl isopeptide prodrugs of teixobactin and teixobactin derivatives.

The antibiotic teixobactin is a promising drug candidate against drug-resistant pathogens, such as MRSA and VRE, but forms insoluble gels that may limit intravenous administration. -Acyl isopeptide prodrug analogues of teixobactin circumvent the problem of gel formation while retaining antibiotic activity. The teixobactin prodrug analogues contain ester linkages between Ile and Ser, Ile and Ser, or between both Ile and Ser and Ile and Ser.

Teixobactin kills bacteria by a two-pronged attack on the cell envelope.

Antibiotics that use novel mechanisms are needed to combat antimicrobial resistance. Teixobactin represents a new class of antibiotics with a unique chemical scaffold and lack of detectable resistance. Teixobactin targets lipid II, a precursor of peptidoglycan.

Elucidating the Oligomerization and Cellular Interactions of a Trimer Derived from Aβ through Fluorescence and Mass Spectrometric Studies.

Aβ oligomers play a central role in the neurodegeneration observed with Alzheimer's disease. Our laboratory has developed covalently stabilized trimers derived from residues 17-36 of Aβ as model systems for studying Aβ oligomers. In the current study, we apply the emerging techniques of fluorescence lifetime imaging microscopy (FLIM) and native mass spectrometry (native MS) to better understand the assembly and interactions of the oligomer model system 2AT-L in aqueous solutions and with cells.

Visualizing the mode of action and supramolecular assembly of teixobactin analogues in .

Teixobactin has been the source of intensive study and interest as a promising antibiotic, because of its excellent activity against drug-resistant Gram-positive pathogens and its novel but not yet fully understood mechanism of action that precludes drug resistance. Recent studies have demonstrated that the mode of action of teixobactin is more complicated than initially thought, with supramolecular assembly of the antibiotic appearing to play a critical role in the binding process. Further studies of the interactions of teixobactin with bacteria and its molecular targets offer the promise of providing deeper insights into its novel mechanism of action and guiding the design of additional drug candidates and analogues.

Enantiomeric β-sheet peptides from Aβ form homochiral pleated β-sheets rather than heterochiral rippled β-sheets.

In 1953, Pauling and Corey postulated "rippled" β-sheets, composed of a mixture of d- and l-peptide strands, as a hypothetical alternative to the now well-established structures of "pleated" β-sheets, which they proposed as a component of all-l-proteins. Growing interest in rippled β-sheets over the past decade has led to the development of mixtures of d- and l-peptides for biomedical applications, and a theory has emerged that mixtures of enantiomeric β-sheet peptides prefer to co-assemble in a heterochiral fashion to form rippled β-sheets. Intrigued by conflicting reports that enantiomeric β-sheet peptides prefer to self-assemble in a homochiral fashion to form pleated β-sheets, we set out address this controversy using two β-sheet peptides derived from Aβ and Aβ, peptides 1a and 1b.

Synthesis and application of fluorescent teixobactin analogs.

Teixobactin is a promising new antibiotic that kills a spectrum of Gram-positive pathogens that are considered to be urgent threats by the CDC and the WHO. Better understanding of the novel mechanism of action of teixobactin may assist in developing new antibiotics and furthering our understanding of antibiotic resistance. This chapter describes the synthesis and application of fluorescent teixobactin analogs in fluorescence microscopy to study the mode of action of teixobactin.

Effects of Familial Alzheimer's Disease Mutations on the Assembly of a β-Hairpin Peptide Derived from Aβ.

Familial Alzheimer's disease (FAD) is associated with mutations in the β-amyloid peptide (Aβ) or the amyloid precursor protein (APP). FAD mutations of Aβ were incorporated into a macrocyclic peptide that mimics a β-hairpin to study FAD point mutations K16N, A21G, E22Δ, E22G, E22Q, E22K, and L34V and their effect on assembly, membrane destabilization, and cytotoxicity. The X-ray crystallographic structures of the four E22 mutant peptides reveal that the peptides assemble to form the same compact hexamer.

Macrocyclic Peptides Derived from Familial Alzheimer's Disease Mutants Show Charge-Dependent Oligomeric Assembly and Toxicity.

This work probes the role of charge in the oligomeric assembly, toxicity, and membrane destabilization of a series of peptides derived from Aβ and the E22Q and E22K familial mutants. In the mutant Aβ peptides, an acidic residue (E) is replaced with either a neutral or basic residue (Q or K), thus altering the net charge of the peptide. Acetylation at peripheral positions permits modulation of charge of the peptides and allows investigation of the role of charge in their oligomeric assembly, cytotoxicity, and membrane disruption.

A Disulfide-Stabilized Aβ that Forms Dimers but Does Not Form Fibrils.

Aβ dimers are a basic building block of many larger Aβ oligomers and are among the most neurotoxic and pathologically relevant species in Alzheimer's disease. Homogeneous Aβ dimers are difficult to prepare, characterize, and study because Aβ forms heterogeneous mixtures of oligomers that vary in size and can rapidly aggregate into more stable fibrils. This paper introduces Aβ as a disulfide-stabilized analogue of Aβ that forms stable homogeneous dimers in lipid environments but does not aggregate to form insoluble fibrils.