FIGURE 2.

Site-specific O-glycosylation modulates the in vitro cleavage of hβ₁AR N-terminal peptides. A, in vitro cleavage analysis of β₁AR peptide I and II and respective glycopeptides by ADAM17 monitored by MALDI-TOF. Products formed after 30-min, 1-h, and 4-h incubations are shown. ADAM17 was able to cleave both the naked peptide and the O-glycopeptide at the ³¹R↓L³² and ⁵²P↓L⁵³ cleavage sites. However, the cleavage of the glycopeptides was less efficient. B, in vitro cleavage analysis of β₁AR peptide I and O-glycopeptide by MMP9. Cleavage was observed at ⁴¹S↓L⁴², and again, the glycopeptide was less efficiently cleaved. C, schematic overview of the total observed cleavage sites by ADAM10, ADAM17, and MMPs, and their relation to the observed glycosylation sites. The boldface font indicates that a protection from cleavage was observed. The spectra show relative intensity. The locations of the attached GalNAcs are shown as gray squares. The results shown are representative of three (A) and two (B) independent experiments.