Identification of glutamine and lysine residues in Alzheimer amyloid beta A4 peptide responsible for transglutaminase-catalysed homopolymerization and cross-linking to alpha 2M receptor.

The beta-amyloid peptide (beta A4), derived from a larger amyloid precursor protein, is the principal component of senile plaques in Alzheimer's disease. Here we report that the full-length (1-40) synthetic beta A4 peptide, containing one glutamine and two lysine residues, is able to form homopolymers in a transglutaminase-mediated reaction. Moreover, transglutaminase catalysed the formation of heteropolymers in reactions of beta A4 with alpha 2M receptor, a constituent of amyloid plaques, and with extracellular matrix proteins. Incorporation of site-specific probes followed by enzymatic digestion and sequencing of tracer-containing fractions demonstrated that both Lys16, Lys28 and Gln15 in beta A4 were susceptible to cross-linking by transglutaminase.