Mannosyl Alpha-1,3-Glycoprotein Beta-1,4-N-Acetylglucosaminyltransferase Isozyme B (MGAT4B)

MGAT4B encodes a key glycosyltransferase that regulates the formation of tri- and multiantennary branching structures in the Golgi apparatus. The encoded protein, in addition to the related isoenzyme A, catalyzes the transfer of N-acetylglucosamine from UDP-GlcNAc in a beta-1,4 linkage to the Man-alpha-1,3-Man-beta-1,4-GlcNAc arm of R-Man-alpha-1,6 Man-beta-1, 4-GlcNAc-beta-1,4-GlcNAc-beta-1-Asn. The protein may play a role in regulating the availability of serum glycoproteins, oncogenesis, and differentiation. The deduced 548-amino acid MGAT4B protein has a predicted type II membrane topology with a short N-terminal cytoplasmic tail. MGAT4A and MGAT4B share 62% amino acid sequence identity. Northern blot analysis detected a 2.7-kb MGAT4B transcript in all human tissues and cancer cell lines tested.