Single Posttranslational Modifications in the Central Repeat Domains of Tau4 Impact its Aggregation and Tubulin Binding

A variety of methods have been employed to study the impact of posttranslational modifications on Tau protein function. Here, a semisynthesis strategy is described that enables selective modification within the central repeat domain of Tau4 (residues 291‐321), comprising a major interaction motive with tubulin as well as one of the key hexapeptides involved in Tau aggregation. This strategy has led to the preparation of four semisynthetic Tau variants with phosphoserine residues in different positions and one with a so far largely ignored carboxymethyllysine modification that results from a non‐enzymatic posttranslational modification (nPTM). The latter modification inhibits tubulin polymerization but exhibits an aggregation behavior very similar to unmodified Tau. In contrast, phosphorylated Tau variants exhibit similar binding to tubulin as unmodified Tau4 but show lower tendencies to aggregate. Underinvestigated protein modifications: Posttranslational modifications and non‐enzymatic posttranslational modifications (nPTMs) within large proteins, such as Tau, are major players in regulating protein activity. The impact of two specific phosphorylation sites, and of the nPTM carboxymethyllysine, within the repeat domains of Tau4, was examined by combining two recombinant segments with a synthetic peptide.