FIGURE 4.

In vivo xylosyltransferase activity. Shown are the MALDI-mass spectra of insect cell-produced EGF1–5 that was co-infected with GLT8D1 as a negative control (A), GXYLT1 (B), or GXYLT2 (C). The glucosylated peptide with the calculated nominal mass of 3498 Da is most dominant in A but is reduced in favor of the Xyl-Glc-peptide (3630 Da) after incubation with GXYLT1 or GXYLT2. As for Fig. 3, peptide sequencing was performed and is presented in supplemental Fig. S2.