* Transfers GlcNAc(α1-4) to βGal preferentially present in O-glycans forming GlcNAc(α1-4)Galβ-R or terminal αGlcNAc.
* The enzyme shows preference to act on core-2 glycan rather than core-1 glycans indicating a role for GlcNAc(β1-6) in promoting its activity. It extends the core-1 arm of O-glycans.
* It can act on both arms of core-2 glycan to corm structures like GlcNAc(α1-4)Gal(β1-4)GlcNAc(β1-6)[GlcNAc(α1-4)Gal(β1-3)]GalNAc.
* A4GNT is expressed in stomach, gall bladder, duodenum, and thus such structures are normally restricted to gland & gastric mucins, particulalry MUC6 with a small amount also being associated with MUC5AC.
* αGlcNAc is also expressed in pancreatic ducts showing gastric metaplasia or pancreatic intraepithelial neoplasia 1 (PanIN-1).
* A4gnt knockout mice revealed that αGlcNAc serves as a tumor suppressor of differentiated type of gastric adenocarcinoma. In addition, αGlcNAc protects gastric gland mucous cells from H. pylori infection. Thus, αGlcNAc plays a dual role to prevent the gastric mucosa from gastric tumorigenesis.