CHST13 catalyses the transfer of sulfate to position 4 of the N-acetylgalactosamine (GalNAc) residue of chondroitin. Its specificity is defined: it transfers sulfate to the C4 hydroxyl of beta-1,4-linked GalNAc that is substituted with a beta-linked glucuronic acid at the C-3 hydroxyl. UniProt reports no activity toward dermatan, which distinguishes its substrate preference from that of other sulfotransferases acting on related glycosaminoglycans.

Chondroitin sulfate is the predominant proteoglycan present in cartilage and is distributed on the surfaces of many cells and within extracellular matrices. Sulfation of the chondroitin chain by enzymes such as CHST13 is therefore a point of interest for researchers studying matrix composition and cell-surface glycosaminoglycans.

The CHST13 protein belongs to the sulfotransferase 2 family and is classed by HGNC in the group of membrane-bound sulfotransferases. It is localised to the Golgi apparatus membrane, where glycosaminoglycan modification takes place. The enzyme carries the EC number 2.8.2.5. The gene was previously named carbohydrate (chondroitin 4) sulfotransferase 13, and C4ST3 remains a common alias. Related family members such as CHST9 are also studied in the context of carbohydrate sulfation.