Oligomer Complexes of the (VQIVYK + NNQQNY) and (VQIVYK + LYQLEN) Mixing Solutions

The ${\pi}-{\pi}$ interactions of the peptide-dimer and peptide-trimer complexes were investigated in the (VQIVYK + LYQLEN) and (VQIVYK + NNQQNY) mixing solutions. The results showed that tyrosine (Y) residues were critical in the formation of hetero peptide-dimers and -trimers during the early oligomerization process. We used collision-induced dissociation (CID) along with electrospray ionization mass spectroscopy (ESI-MS) to obtain the structural information of the hetero-dimers and -trimers. We chose three amyloidogenic peptides-VQIVYK, NNQQNY, and LYQLEN-from tau protein, yeast prion-like protein Sup35, and insulin chain A, respectively. Hetero-dimer, -trimer, -tetramer, and -pentamer complexes were observed in the mass spectra. The tandem mass spectrum of the hetero-dimer and hetero-trimer showed two different fragmentation patterns (covalent and non-covalent bond dissociation). Y-Y interaction structures were also proposed for the hetero-dimer and -trimer complexes.