FIG. 2.

Peptide mapping analysis of phosphorylated wild-type and mutant β4 integrin. Excised bands containing ³²P-radiolabeled wild-type β4 from HaCat cells (A) or mutated β4 from COS-7 transfectants (B to D) were digested using trypsin, and the peptides were resolved in two dimensions using a combination of TLE and TLC and exposed to a phosphor screen. The phosphopeptides of interest for this study (pp₀, pp₁, and pp₂) are located below a line defined by a control dye. Notice the disappearance of pp₀ and both an increase and relocation of pp₁ and pp₂ to more hydrophobic (higher) positions in β4_S1356A (B); the disappearance of pp₀ and pp₁, as well as the relocation of pp₂ to a more hydrophilic (lower) position in the double mutant β4_{S1356D S1360D} (C); and the disappearance of pp₀, pp₁, and pp₂ in the triple mutant β4_{S1356D S1360D S1364D} (D).