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. 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. Belongs to the KDELC family.