1oqm
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A 1:1 complex between alpha-lactalbumin and beta1,4-galactosyltransferase in the presence of UDP-N-acetyl-galactosamine
OverviewOverview
beta1,4-Galactosyltransferase I (Gal-T1) normally transfers Gal from, UDP-Gal to GlcNAc in the presence of Mn(2+) ion. In the presence of, alpha-lactalbumin (LA), the Gal acceptor specificity is altered from, GlcNAc to Glc. Gal-T1 also transfers GalNAc from UDP-GalNAc to GlcNAc, but, with only approximately 0.1% of Gal-T activity. To understand this low, GalNAc-transferase activity, we have carried out the crystal structure, analysis of the Gal-T1.LA complex with UDP-GalNAc at 2.1-A resolution. The, crystal structure reveals that the UDP-GalNAc binding to Gal-T1 is similar, to the binding of UDP-Gal to Gal-T1, except for an additional hydrogen, bond formed between the N-acetyl group of GalNAc moiety with the Tyr-289, side chain hydroxyl group. Elimination of this additional hydrogen bond by, mutating Tyr-289 residue to Leu, Ile, or Asn enhances the, GalNAc-transferase activity. Although all three mutants exhibit enhanced, GalNAc-transferase activity, the mutant Y289L exhibits GalNAc-transferase, activity that is nearly 100% of its Gal-T activity, even while completely, retaining its Gal-T activity. The steady state kinetic analyses on the, Leu-289 mutant indicate that the K(m) for GlcNAc has increased compared to, the wild type. On the other hand, the catalytic constant (k(cat)) in the, Gal-T reaction is comparable with the wild type, whereas it is 3-5-fold, higher in the GalNAc-T reaction. Interestingly, in the presence of LA, these mutants also transfer GalNAc to Glc instead of to GlcNAc. The, present study demonstrates that, in the Gal-T family, the Tyr-289/Phe-289, residue largely determines the sugar donor specificity.
About this StructureAbout this Structure
1OQM is a Protein complex structure of sequences from Bos taurus and Mus musculus with CA, MN, UD2 and PG4 as ligands. This structure superseeds the now removed PDB entry 1L7W. Active as Beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase, with EC number 2.4.1.38 Full crystallographic information is available from OCA.
ReferenceReference
Structure-based design of beta 1,4-galactosyltransferase I (beta 4Gal-T1) with equally efficient N-acetylgalactosaminyltransferase activity: point mutation broadens beta 4Gal-T1 donor specificity., Ramakrishnan B, Qasba PK, J Biol Chem. 2002 Jun 7;277(23):20833-9. Epub 2002 Mar 26. PMID:11916963
Page seeded by OCA on Tue Nov 20 23:06:31 2007