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). L-seryl-[protein] + UDP-N-acetyl-alpha-D-galactosamine = 3-O-[N-acetyl-alpha-D-galactosaminyl]-L-seryl-[protein] + H(+) + UDP L-threonyl-[protein] + UDP-N-acetyl-alpha-D-galactosamine = 3-O-[N-acetyl-alpha-D-galactosaminyl]-L-threonyl-[protein] + H(+) + UDP Protein modification; protein glycosylation. Interacts with NOTCH1. Highly expressed in kidney. Expressed at intermediate level in brain, heart and skeletal muscle. Weakly expressed other tissues. In kidney, it is strongly expressed in tubules but not expressed in glomeruli. There are two conserved domains in the glycosyltransferase region: the N-terminal domain (domain A, also called GT1 motif), which is probably involved in manganese coordination and substrate binding and the C-terminal domain (domain B, also called Gal/GalNAc-T motif), which is probably involved in catalytic reaction and UDP-Gal binding. The ricin B-type lectin domain binds to GalNAc and contributes to the glycopeptide specificity. Defects in GALNT11 may be a cause of heterotaxy, a congenital heart disease resulting from abnormalities in left-right (LR) body patterning. Belongs to the glycosyltransferase 2 family. GalNAc-T subfamily. Truncated N-terminus. Polypeptide N-acetylgalactosaminyltransferase 11