PMC

ESI-MS analysis of cross-linked Aβ_1–25 dimer. TGase cross-linking of a Aβ_1–25 peptide fragment (monoisotopic mass = 2931.36 Da) increases the formation of stable dimers, because this fragment peptide lacks Lys²⁸ for competitive, intramolecular cross-linking. Above, calculated theoretical isotopic cluster of WT Aβ_1–25 dimer (black cluster, m/z = 1173.6[M+5H]⁵⁺), calculated cluster of cross-linked (cl) Aβ_1–25 dimer with deamidation at the second Gln¹⁵ (gray cluster, m/z 1170.3[M+5H]⁵⁺), and cross-linked Aβ_1–25 dimer without deamidation (white cluster, 1170.1[M+5H]⁵⁺). Below, high resolution ESI-MS analysis of the isotopic cluster from in vitro TGase cross-linked Aβ_1–25 dimers, of which the isotopic mass (m/z = 1170.32[M+5H]⁵⁺) corresponds to the mass of 2(2931.36 Da) to (17.026 Da (NH₃)), of which the second Gln¹⁵ is deamidated to Glu¹⁵ + (0.984 Da). Inset, MS/MS fragmentation of the cross-linked Aβ_1–25 dimer. The presence of abundant b ions confirmed the identity of this cross-linked fragment peptide, of which ion b₇ is always readily observed by CID fragmentation. Larger fragments involved the loss of C-terminal residues Ala²¹ to Gly²⁵ within a whole Aβ_1–25 dimer (dimer (D))-(21–25). A summary of all identified ions is depicted in the adjacent diagram. For the sake of simplicity fragment ions are only depicted on one side of the dimer, but could take place on either the monomer or a combination of both. The scheme of the cross-linked dimer shows a deamidation at position Glu¹⁵ (-NH₂ +OH), whereas Gln¹⁵ on the lower monomer serves for cross-linking (transamidation: -NH₃) with Lys¹⁶ and hence accounts for stabilization of the dimer.

Schematic representation of (A) heterogeneously cross-linked EPM-g-furan and (B) homogeneously cross-linked EVM-g-furan.

(A) TD-NMR MQ buildup and reference signals for BM cross-linked EVM-g-furan. The uncorrected, normalized MQ curve is highlighted using solid dots. (B) Residual dipolar coupling distribution obtained by fitting the corrected MQ curves for BM cross-linked EPM-g-furan and EVM-g-furan.

Median stress–strain curves of (A) EPM-g-furan and EVM-g-furan, their BM cross-linked products, and DCP cured EPM and EVM references at similar cross-link density at a strain rate of 500 mm/min and (B) BM cross-linked EPM-g-furan and EVM-g-furan at strain rates of 5 and 500 mm/min.