Catalyzes the transfer of Gal to GlcNAc-based acceptors with a preference for the core3 O-linked glycan GlcNAc(beta1,3)GalNAc structure. Can use glycolipid LC3Cer as an efficient acceptor. Also catalyzes the transfer of Gal to the terminal GalNAc unit of the globoside GB4, thereby synthesizing the glycolipid GB5, also known as the stage-specific embryonic antigen-3 (SSEA-3). globoside Gb4Cer (d18:1(4E)) + UDP-alpha-D-galactose = globoside GalGb4Cer (d18:1(4E)) + H(+) + UDP Protein modification; protein glycosylation. Expressed in brain and kidney. Belongs to the glycosyltransferase 31 family. b3GalT5