Terminal galactose residues on cell-surface glycoconjugates (Terminal Gal)

Terminal galactose residues are carbohydrate motifs located at the non-reducing ends of glycan chains on cell-surface glycoproteins and glycolipids. They play a pivotal role in the circulatory half-life of glycoproteins; the exposure of these residues through the removal of terminal sialic acid (desialylation) serves as a biological signal for hepatic clearance via the Ashwell-Morell receptor, also known as the asialoglycoprotein receptor (ASGPR) (Ashwell & Morell, 1974) [1]. In pathological states such as cancer, altered terminal galactose expression is frequently observed, contributing to tumor cell adhesion, migration, and immune evasion (Pinho & Reis, 2015) [2]. These residues are also the primary targets for potent plant toxins like ricin and abrin, which utilize the galactose-binding B-chain to gain entry into the host cell cytosol (Lord et al., 2003) [3]. In modern drug development, terminal galactose and its derivatives (such as GalNAc) are extensively utilized as targeting moieties to deliver oligonucleotides and nanoparticles specifically to the liver (Springer & Dowdy, 2018) [4]. Furthermore, they interact with the galectin family of proteins to regulate various inflammatory and immune signaling pathways (Liu & Rabinovich, 2005) [5].

Other names

Terminal galactoseGalactose-terminated glycansExposed galactose residuesDesialylated glycoconjugatesNon-reducing terminal galactose

Terminal galactose residues act as high-affinity ligands for the asialoglycoprotein receptor (ASGPR) on hepatocytes, triggering clathrin-mediated endocytosis for the clearance of desialylated proteins. They also serve as primary attachment sites for AB-type toxins (e.g., ricin) and bacterial adhesins (e.g., from Pseudomonas aeruginosa), facilitating cellular entry. Additionally, they function as ligands for endogenous galectins, which modulate immune responses and cell-matrix interactions.