Fig. 1.

C100Spitz-Flag substrate is cleaved at two intramembrane sites. Pure C100Spitz-Flag was incubated for 2 h at 37°C with GlpG or buffer alone, and the C-terminal cleavage products were captured and analyzed in parallel by MALDI-TOF mass spectrometry (Left) and Western blot (Upper Right). The predicted mass of intact C100Spitz-Flag is 12,166 Da. The Spitz substrate motif (bracketed) is shown, with an external lysine N-terminal to the transmembrane domain above. Predicted masses of cleavage products designated by arrows are shown, and they correspond well to the peaks that appear in the mass spectrum after incubation with GlpG but not buffer alone.