Synthesis of chemically-tethered amyloid-β segment trimer possessing amyloidogenic properties

Abstract

As amyloid-β (Aβ) undergoes dynamic aggregation, it is impossible to isolate ('hook') the transient Aβ oligomer in an assembly state-pure form (e.g., sole Aβ dimer, trimer, tetramer, etc.). Obtaining such a pure Aβ oligomer would allow us to establish an in vitro system to perform a more detailed investigation of the pathogenic properties of the oligomer. A chemically-tethered Aβ oligomer, constructed only by covalent bonds, could satisfy this demand. Here we designed a chemically-tethered trimer of a pathogenic Aβ fragment (Aβ25-35) (1) and successfully generated it in situ from its precursor (4), a water-soluble and non-aggregative O-acyl isopeptide of 1, in neutral aqueous media. Chemically-tethered 1 possessed stronger amyloidogenic properties, that is, potential for β-sheet structure, fibril formation, and cytotoxicity, than the corresponding monomer Aβ25-35 (6). Trimerization of Aβ25-35 sequence might affect both the aggregative properties and cytotoxicity, based on the present results. This work opens the door for chemical synthesis of oligomers bigger than trimers in an assembly state-pure form, allowing for identification of the most toxic Aβ oligomer.

Monoclonal antibody with conformational specificity for a toxic conformer of amyloid β42 and its application toward the Alzheimer’s disease diagnosis

“…Dimers, trimers, and tetramers of Aβ42, as prepared by photo-induced cross-linking of unmodified protein (PICUP) technology using 2,2′-bipyridyl-dichlororuthenium(II) hexahydrate as a catalyst, were mainly bound covalently at Tyr10 40 , although it seems difficult to isolate these oligomers in a pure form. Recently, unique synthesis of N-terminal-tethered triple Aβ fragment (Aβ25–35) has been reported 41 as a trimeric model, which may be another minimal unit of toxic oligomers (2 or 3 × n -mer) of Aβ42. When we take into account these models as candidates of toxic oligomers, further investigation will be required to clarify the significance in vivo , though the pathology of the genetically modified mice to produce Aβ dimer cross-linked at Ser8 in N-terminal region was recently reported 42 .…”

Evaluation of Met-Val-Lys as a Renal Brush Border Enzyme-Cleavable Linker to Reduce Kidney Uptake of 68Ga-Labeled DOTA-Conjugated Peptides and Peptidomimetics

“…Synthesis of Fmoc-Lys(pentynoyl)-OtBu (2) is shown in Scheme 1. Fmoc-Lys(pentynoyl)-OH (1) prepared from literature procedures [17] was reacted with 2,2,2-trichloroacetimidate (2.2 equiv) in CH 2 Cl 2 . After overnight incubation at room temperature and purification by flash column chromatography, the desired product 2 was obtained in 79% yield.…”

Covalent Tethering and Residues with Bulky Hydrophobic Side Chains Enable Self‐Assembly of Distinct Amyloid Structures

“…In addition to intramolecular covalent tethering, various intermolecular dimeric disulfide‐linked Aβ constructs have been produced; these differed in fiber formation kinetics and exhibited biological effects previously undetected for wild‐type Aβ . More recently, a construct was synthesized, in which a cyclic peptide served to display three copies of the amyloidogenic [25–35] Aβ fragment; this construct exhibited enhanced aggregation and cytotoxicity …”