Catalyzes the addition of sialic acid in alpha 2,8-linkage to the sialic acid moiety of the ganglioside GM3 to form ganglioside GD3; gangliosides are a subfamily of complex glycosphingolipds that contain one or more residues of sialic acid (By similarity). Can catalyze the addition of a second alpha-2,8- sialic acid to GD3 to form GT3 (By similarity). Can use GM1b, GD1a and GT1b as acceptor substrates to synthesize GD1c, GT1a and GQ1b respectively (By similarity).
Subcellular locations: Golgi apparatus membrane