Recombinant Human CHST15 Protein, CF

N‑Acetylgalactosamine 4‑sulfate 6‑O‑sulfotransferase (GalNAc4S‑6ST, or, CHST15) is a type II transmembrane protein composed of a short N‑terminal cytoplasmic domain and a long C‑terminal luminal catalytic domain. GalNAc4S‑6ST transfers sulfate from 3'‑phosphoadenosine 5'‑phosphosulfate (PAPS) to the 6‑O of GalNAc‑4S on chondroitin sulfate A (CS‑A), as well as dermatan sulfate (1), generating the chondroitin sulfate E (CS‑E) disaccharide unit GlcA beta1‑3GalNAc‑4S,6S. CS‑E binds with strong affinity to Midkine, a heparan sulfate‑binding growth factor (2), playing an important regulatory role in differentiation and morphogenesis during embryonic development. In situ hybridization for the expression of GalNAc4S‑6ST in the postnatal mouse brain showed a widespread expression of the transcript in the developing brain except at postnatal day 7 (3). For comparison, chondroitin sulfate 6‑O sulfotransferase‑1 (C6ST‑1) encoded by the CHST3 gene, only recognizes and transfers sulfate to the 6‑O of unsulfated GalNAc residues on chondroitin sulfate generating the chondroitin sulfate C (CS‑C) disaccharide unit GlcA beta1‑3GalNAc‑6S (4). The sequence of the human GalNAc4S‑6ST was found to be the same as human B‑cell RAG‑associated protein (BRAG) (1). The activity of the recombinant human CHST15 is measured using a PAP-specific phosphatasecoupled sulfotransferase assay (5).