Probing the impact of posttranslational modifications on peptide and protein aggregation: Semi-Synthesis of the Alzheimer-relevant Tau Protein
In this project we are studying the structural consequences of posttranslational modification on model peptide sequences. Building upon recent model studies, in which we studied the impact of phosphorylation on aggregating coiled-coils or β-sheets, we also focus on studying the effect of phosphorylation and glycosylation on intrinsically unstructured proteins. A prime example is the neuronal Tau protein, which exists in an unstructured soluble form, a microtubule bound state of unknown structure, or a hyperphosphorylated aggregated state found in neurofibrillar tangles in Alzheimer’s disease.
Currently, we are investigating the complex relation between phosphorylation and aggregation of Tau by generating otherwise non-accessible homogeneously phosphorylated proteins using protein semi-synthesis. Very recently, we have succeeded in the first semi-synthesis of a homogeneously phosphorylated functional Tau protein. Furthermore, we extend this study to glycosylated Tau to evaluate whether a perturbed balance between phosphorylation and glycosylation (O-GlcNAc) is associated with Tau aggregation. Other studies (with Guy Lippens, CNRS Lille), in which synthetic phosphorylated peptides were subjected to enzymatic transformations, have already identified two new O-GlcNAc glycosylation sites in Tau and furthermore demonstrated the reciprocal relationship between phosphorylation and O-GlcNAcylation.