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. Can also catalyze the transfer of xylose from UDP-xylose but less efficiently. Specifically targets extracellular EGF repeats of proteins such as NOTCH1, NOTCH3, FBN1, FBN2 and LTBP1. May regulate the transport of NOTCH1 and NOTCH3 to the plasma membrane and thereby the Notch signaling pathway. L-seryl-[EGF-like domain protein] + UDP-alpha-D-glucose = 3-O-(beta-D-glucosyl)-L-seryl-[EGF-like domain protein] + H(+) + UDP L-seryl-[EGF-like domain protein] + UDP-alpha-D-xylose = 3-O-(beta-D-xylosyl)-L-seryl-[EGF-like domain protein] + H(+) + UDP Protein modification; protein glycosylation. Widely expressed. Expressed in various fetal tissues. N-glycosylated. Belongs to the KDELC family.