1nmm: Difference between revisions

Revision as of 15:07, 21 February 2008

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 , and as ligands. This structure supersedes 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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 '''beta-1,4-galactosyltransferase mutant Cys342Thr complex with alpha-lactalbumin and GlcNAc'''<br />
 ==Overview==
-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.
+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 Structure==
-NMM is a [http://en.wikipedia.org/wiki/Protein_complex Protein complex] structure of sequences from [http://en.wikipedia.org/wiki/Bos_taurus Bos taurus] and [http://en.wikipedia.org/wiki/Mus_musculus Mus musculus] with NAG, CA and PG4 as [http://en.wikipedia.org/wiki/ligands ligands]. This structure superseeds the now removed PDB entry 1JN8. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1NMM OCA].
+NMM is a [http://en.wikipedia.org/wiki/Protein_complex Protein complex] structure of sequences from [http://en.wikipedia.org/wiki/Bos_taurus Bos taurus] and [http://en.wikipedia.org/wiki/Mus_musculus Mus musculus] with <scene name='pdbligand=NAG:'>NAG</scene>, <scene name='pdbligand=CA:'>CA</scene> and <scene name='pdbligand=PG4:'>PG4</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. This structure supersedes the now removed PDB entry 1JN8. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1NMM OCA].
 ==Reference==
@@ Line 14: / Line 14: @@
 [[Category: Mus musculus]]
 [[Category: Protein complex]]
-[[Category: Qasba, P.K.]]
+[[Category: Qasba, P K.]]
 [[Category: Ramakrishnan, B.]]
-[[Category: Shah, P.S.]]
+[[Category: Shah, P S.]]
 [[Category: CA]]
 [[Category: NAG]]
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 [[Category: cys342thr mutation]]
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