BtaEX0038728 @ bosTau6

The UDP-N-acetylhexosamine (UDP-HexNAc) pyrophosphorylase AGX has two isoforms: AGX1 and AGX2. AGX2 is identical in sequence to AGX1 except that it has a 17-amino acid insert near the carboxyl terminus (encoded by HsaEX0068590). The authors expressed the AGX1 and AGX2 genes in Escherichia coli. The protein isolated from the AGX1 clone comigrated on SDS gels with the liver 57-kDa pyrophosphorylase subunit and was 2?3 times more active with GalNAc-1-P than with GlcNAc1-P. On the other hand, the protein from the AGX2 clone migrated with the liver 64-kDa pyrophosphorylase subunit and had 8-fold better activity with GlcNAc-1-P than with GalNAc-1-P

The human UDP-N-acetylglucosamine (UDPGlcNAc) pyrophosphorylases AGX1 and AGX2, which differ in sequence by an alternatively spliced 17 residue peptide (encoded by HsaEX0068590, included in AGX2), are key enzymes synthesizing UDPGlcNAc, an essential precursor for protein glycosylation. To better understand the catalytic mechanism of these enzymes and the role of the alternatively spliced segment, the authors have solved the crystal structures of AGX1 and AGX2 in complexes with UDPGlcNAc (at 1.9 and 2.4 _ resolution, respectively) and UDPGalNAc (at 2.2 and 2.3 _ resolution, respectively). Comparison with known structures classifies AGX1 and AGX2 as two new members of the SpsA-GnT I Core superfamily and, together with mutagenesis analysis, helps identify residues critical for catalysis. Most importantly, these combined structural and biochemical data provide evidence for a change in the oligomeric assembly accompanied by a significant modification of the active site architecture, a result suggesting that the two isoforms generated by alternative splicing may have distinct catalytic properties. Note, the study doesn't identify differences in substrate affinity that is reported in PMID: 9765219.