Traceless purification and desulfurization of tau protein ligation products.

We present a novel strategy for the traceless purification and synthetic modification of peptides and proteins obtained by native chemical ligation. The strategy involves immobilization of a photocleavable semisynthetic biotin-protein conjugate on streptavidin-coated agarose beads, which eliminates the need for tedious rebuffering steps and allows the rapid removal of excess peptides and additives. On-bead desulfurization is followed by delivery of the final tag-free protein product. The strategy is demonstrated in the isolation of a tag-free Alzheimer's disease related human tau protein from a complex EPL mixture as well as a triphosphorylated peptide derived from the C-terminus of tau.