Fig. 2.

Regulation of HNK-1 expression in cells. a Complex of HNK-1-related enzymes comprising β4GalT2, GlcAT-P(S) and HNK-1ST. This specialized complex may work for efficient biosynthesis of HNK-1 carbohydrate. b Two GlcAT-P isoforms. The longer isoform has an additional 13 amino acids in its cytosolic tail. A dibasic motif exists in the cytosolic tail in both isoforms. c Distinct ER exiting processes for two GlcAT-P isoforms. The short isoform can be easily bound by Sar1 to be conveyed from the ER to Golgi, which results in higher intracellular activity in the Golgi. In the case of the long form, the additional 13 amino acids weaken the interaction between Sar1 and the dibasic motif, which retains GlcAT-P in the ER leading to lower intracellular activity