Protein glucosyltransferase that catalyzes the transfer of glucose from UDP-glucose to a serine residue within the consensus sequence peptide C-X-N-T-X-G-S-F-X-C (PubMed:30127001). Can also catalyze the transfer of xylose from UDP-xylose but less efficiently (PubMed:30127001). Specifically targets extracellular EGF repeats of proteins such as NOTCH1, NOTCH3, FBN1, FBN2 and LTBP1 (PubMed:30127001, PubMed:34411563). May regulate the transport of NOTCH1 and NOTCH3 to the plasma membrane and thereby the Notch signaling pathway (PubMed:30127001). {ECO:0000269|PubMed:30127001, ECO:0000269|PubMed:34411563}. This is the function of POGLUT3 (protein O-glucosyltransferase 3, Ensembl gene identifier ENSG00000178202).