1nmm
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beta-1,4-galactosyltransferase mutant Cys342Thr complex with alpha-lactalbumin and GlcNAc
OverviewOverview
beta-1,4-Galactosyltransferase 1 (Gal-T1) transfers galactose (Gal) from, UDP-Gal to N-acetylglucosamine (GlcNAc), which constitutes its normal, galactosyltransferase (Gal-T) activity. In the presence of, alpha-lactalbumin (LA), it transfers Gal to Glc, which is its lactose, synthase (LS) activity. It also transfers glucose (Glc) from UDP-Glc to, GlcNAc, constituting the glucosyltransferase (Glc-T) activity, albeit at, an efficiency of only 0.3-0.4% of Gal-T activity. In the present study, we, show that LA increases this activity almost 30-fold. It also enhances the, Glc-T activity toward various N-acyl substituted glucosamine acceptors., Steady state kinetic studies of Glc-T reaction show that the K(m) for the, donor and acceptor substrates are high in the absence of LA. In the, presence of LA, the K(m) for the acceptor substrate is reduced 30-fold, whereas for UDP-Glc it is reduced only 5-fold. In order to understand this, property, we have determined the crystal structures of the Gal-T1.LA, complex with UDP-Glc x Mn(2+) and with N-butanoyl-glucosamine, (N-butanoyl-GlcN), a preferred sugar acceptor in the Glc-T activity. The, crystal structures reveal that although the binding of UDP-Glc is quite, similar to UDP-Gal, there are few significant differences observed in the, hydrogen bonding interactions between UDP-Glc and Gal-T1. Based on the, present kinetic and crystal structural studies, a possible explanation for, the role of LA in the Glc-T activity has been proposed.
About this StructureAbout this Structure
1NMM is a Protein complex structure of sequences from Bos taurus and Mus musculus with NAG, CA and PG4 as ligands. This structure superseeds the now removed PDB entry 1JN8. Full crystallographic information is available from OCA.
ReferenceReference
alpha-Lactalbumin (LA) stimulates milk beta-1,4-galactosyltransferase I (beta 4Gal-T1) to transfer glucose from UDP-glucose to N-acetylglucosamine. Crystal structure of beta 4Gal-T1 x LA complex with UDP-Glc., Ramakrishnan B, Shah PS, Qasba PK, J Biol Chem. 2001 Oct 5;276(40):37665-71. Epub 2001 Aug 2. PMID:11485999
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