Altered tubulin assembly dynamics with N-homocysteinylated human 4R/1N tau in vitro

► We modified tau by N-homocysteinylation (0.15, 1.5 and 15mM). ► We found that 25 Lys residues are particularly susceptible to modification in the presence of 15mM tHcy. ► Binding of tau to MTP is inhibited upon modification, depending on the degree of N-homocysteinylation. ► N-Hcy-tau species, compared to unmodified tau, change the assembly parameters, critical concentration and morphology of MTP. Tau isoforms promote neuronal integrity through binding and stabilization of microtubule proteins (MTP). It has been shown that hyperphosphorylation of tau contributes to Alzheimer’s disease (AD) pathology and related tauopathies. However, other pathogenic modifications of tau have not been well characterized. It is well accepted that elevated level of homocysteine (Hcy) is associated with neurodegenerative diseases such as AD. As a result of N-homocysteinylation of lysine residues, Hcy becomes a component of proteins, as a protein–homocystamide adduct, which affects protein structure and function. Here we demonstrate that N-homocysteinylation of human tau (4R/1N isoform) inhibits its function via impaired tau–tubulin specific binding and MTP assembly dynamics in vitro.