N-linked oligosaccharides on the low density lipoprotein receptor homolog SorLA/LR11 are modified with terminal GalNAc-4-SO₄ in kidney and brain

Sorting protein-related receptor (SorLA/LR11) is a highly conserved mosaic receptor that is expressed by cells in a number of different tissues including principal cells of the collecting ducts in the kidney and neurons in the central and peripheral nervous systems. SorLA/LR11 has features that indicate it serves as a sorting receptor shuttling between the plasma membrane, endosomes, and the Golgi. We have found that a fraction of SorLA/LR11 that is synthesized in the kidney and the brain bears N-linked oligosaccharides that are modified with terminal β1,4-linked GalNAc-4-SO₄. Oligosaccharides located in the vacuolar sorting (Vps) 10p domain (Vps10p domain) are modified with β1,4-linked GalNAc when the Vps10p domain is expressed in cells along with either of two recently cloned protein-specific β1,4GalNAc-transferases, GalNAcTIII and GalNAcTIV. Either of two sequences with basic amino acids located within the Vps10p domain is able to mediate recognition by these β1,4GalNAc-transferases. The highly specific modification of oligosaccharides in the Vps10p domain of SorLA/LR11 with terminal GalNAc-4-SO₄ suggests that this unusual modification may modulate the interaction of SorLA/LR11 with proteins and influence their trafficking.