FIGURE 3.

α4 cleavage occurs at the Phe²⁵⁵-Gly²⁵⁶ bond. A, coverage map of the full-length α4 and cleaved α4 peptides determined by mass spectrometry. Closed boxes mark peptide regions identified in full-length FLAG-α4; open boxes mark peptide regions identified in the FLAG-α4 cleavage product. The residues highlighted in gray correspond to the unique peptide found only in the α4 cleavage product. The MS spectrum for this peptide can be found in supplemental Fig. S2. B, HEK293FT cells expressing empty vector (EV), wild type FLAG-α4 (WT), or FLAG-α4 1–255 (G256*) were analyzed by Western using an α4-specific antibody.