Dual specificity glycosyltransferase that catalyzes the transfer of glucose and xylose from UDP-glucose and UDP-xylose, respectively, to a serine residue found in the consensus sequence of C-X-S-X-P-C. Specifically targets extracellular EGF repeats of protein such as CRB2, F7, F9 and NOTCH2 (By similarity). Acts as a positive regulator of Notch signaling by mediating O-glucosylation of Notch, leading to regulate muscle development (By similarity). Notch glucosylation does not affect Notch ligand binding (By similarity). Required during early development to promote gastrulation: acts by mediating O-glucosylation of CRB2, which is required for CRB2 localization to the cell membrane (By similarity). L-seryl-[EGF-like domain protein] + UDP-alpha-D-xylose = 3-O-(beta-D-xylosyl)-L-seryl-[EGF-like domain protein] + H(+) + UDP L-seryl-[EGF-like domain protein] + UDP-alpha-D-glucose = 3-O-(beta-D-glucosyl)-L-seryl-[EGF-like domain protein] + H(+) + UDP Protein modification; protein glycosylation. Belongs to the glycosyltransferase 90 family.