The function of Ensembl gene identifier ENSG00000177511 (ST8SIA3, ST8 alpha-N-acetyl-neuraminide alpha-2,8-sialyltransferase 3) is as follows. Catalyzes the transfer of sialic acid from a CMP-linked sialic acid donor onto a terminal alpha-2,3-, alpha-2,6-, or alpha-2,8- linked sialic acid of an acceptor, such as N-linked oligosaccharides of glycoproteins and glycolipids through alpha-2,8-linkages (PubMed:10766765, PubMed:26192331, PubMed:9826427). Forms oligosialic and polysialic acid on various sialylated N-acetyllactosamine oligosaccharides of glycoproteins, including FETUB N-glycans, a2-HS- glycoprotein (AHSG) and alpha 2,3-sialylated glycosphingolipids, such as alpha 2,3-sialylparagloboside and ganglioside GM3 and to a lesser extent NCAM1 N-glycans (PubMed:10766765, PubMed:9826427). However, it is much more specific to N-linked oligosaccharides of glycoproteins than glycosphingolipids (By similarity). 2,3-sialylparagloboside serves as the best acceptor substrate among the glycolipids (By similarity). alpha-Neu5Ac-(2->8)-alpha-Neu5Ac-(2->3)-beta-D-Gal-(1->4)-6S-D-GlcNAc and monosialyl and disialyl N-acetyllactosamines are the best acceptor substrates among glycoproteins (PubMed:10766765, PubMed:26192331). May play a critical role in the striatum by mediating the formation of disialylated and trisialylated terminal glycotopes on N- and O-glycans of specific striatal proteins, regulating their distribution in lipid rafts, affecting their interaction with other binding partners, and subsequently modulating striatal functions (By similarity). {ECO:0000250|UniProtKB:Q64689, ECO:0000269|PubMed:10766765, ECO:0000269|PubMed:26192331, ECO:0000269|PubMed:9826427}.