a
In vitro POGLUT1 enzymatic assays showed that the activities of the R183W and Y57C mutant versions of POGLUT1 are lower than the activity of WT POGLUT1 (from 3 biological replicates; each assay was performed in triplicate; Supplementary Source Data 2, online resource); b-e Notch1 EGF1–18-MycHis secretion from WT HEK293T cells (clone AB3) or POGLUT1 KO HEK293T cells (clone OD3). Secretion was rescued fully by co-expression of plasmids encoding WT, but not by the indicated mutant versions of POGLUT1. Numbers below refer to micrograms of POGLUT1 plasmid used. A plasmid encoding IgG was co-transfected as secretion control, since IgG is not affected by loss of POGLUT1. Red channel, anti-Myc antibody. Green channel, anti-IgG antibody. Migration positions of Notch1 EGF1–18-MycHis (mN1), POGLUT1-Myc-His, and IgG are indicated.