Past residue 95 alpha-synuclein changes character entirely. The C-terminal third is strongly acidic, stays disordered even within mature fibrils, and acts to keep the protein soluble rather than to drive assembly. This peptide covers residues 91 to 110, spanning the end of the aggregation core and the start of that tail. Removing the tail accelerates aggregation. C-terminal truncation is observed in pathological material and is understood to act by stripping away the solubilising region, so truncated and full-length species behave differently and are distinguished in disease studies. The region also carries the principal post-translational modification sites associated with pathology and is where several widely used antibodies bind. That gives this peptide a specific diagnostic use: establishing whether an antibody requires the intact C-terminus, and therefore whether it will detect truncated species at all. A reagent that fails against this peptide but succeeds against full-length protein is reading something else. Note that the stretch between this peptide and the one ending at residue 70 is not covered by this series, so an antibody negative across the whole set may bind an uncovered window rather than a conformational epitope. | 