Figure 5.

Caspase-6 cleaves tau N terminally in vitro at amino acid D13. A, Caspase-6 treatment of tauΔ422-441 causes the appearance of a single lower molecular weight band recognized by Tau-5 but not by Tau-12 or 5A6. B, Tyrosine phosphorylation at residue 18 of tau by Fyn (top) has little effect on the extent of caspase-6 cleavage as shown by Tau-5 Western blotting (bottom). C, MALDI-TOF mass spectra of in-solution tryptic digests of samples in A show a shift of the peaks at m/z 2053.9 and 2181.9 to 1046.5 and 1174.6 (arrows), respectively, as would be expected for cleavage at D13. All peaks labeled in the spectra correspond to predicted tryptic peptides of tauΔ422-441.