The function of GALNT11 (polypeptide N-acetylgalactosaminyltransferase 11, Ensembl gene identifier ENSG00000178234) is as follows. Polypeptide N-acetylgalactosaminyltransferase that catalyzes the initiation of protein O-linked glycosylation and is involved in left/right asymmetry by mediating O-glycosylation of NOTCH1. O- glycosylation of NOTCH1 promotes activation of NOTCH1, modulating the balance between motile and immotile (sensory) cilia at the left-right organiser (LRO). Polypeptide N-acetylgalactosaminyltransferases catalyze the transfer of an N-acetyl-D-galactosamine residue to a serine or threonine residue on the protein receptor. Displays the same enzyme activity toward MUC1, MUC4, and EA2 than GALNT1. Not involved in glycosylation of erythropoietin (EPO). {ECO:0000269|PubMed:11925450, ECO:0000269|PubMed:16207894, ECO:0000269|PubMed:24226769}.