1nwg
From Proteopedia
(New page: 200px<br /><applet load="1nwg" size="450" color="white" frame="true" align="right" spinBox="true" caption="1nwg, resolution 2.32Å" /> '''BETA-1,4-GALACTOSYLT...) |
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| - | [[Image:1nwg.gif|left|200px]]<br /><applet load="1nwg" size=" | + | [[Image:1nwg.gif|left|200px]]<br /><applet load="1nwg" size="350" color="white" frame="true" align="right" spinBox="true" |
caption="1nwg, resolution 2.32Å" /> | caption="1nwg, resolution 2.32Å" /> | ||
'''BETA-1,4-GALACTOSYLTRANSFERASE COMPLEX WITH ALPHA-LACTALBUMIN AND N-BUTANOYL-GLUCOAMINE'''<br /> | '''BETA-1,4-GALACTOSYLTRANSFERASE COMPLEX WITH ALPHA-LACTALBUMIN AND N-BUTANOYL-GLUCOAMINE'''<br /> | ||
==Overview== | ==Overview== | ||
| - | beta-1,4-Galactosyltransferase 1 (Gal-T1) transfers galactose (Gal) from | + | 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== | ==About this Structure== | ||
| - | 1NWG 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 CA and BGN as [http://en.wikipedia.org/wiki/ligands ligands]. This structure | + | 1NWG 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=CA:'>CA</scene> and <scene name='pdbligand=BGN:'>BGN</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. This structure supersedes the now removed PDB entry 1JNA. Active as [http://en.wikipedia.org/wiki/N-acetyllactosamine_synthase N-acetyllactosamine synthase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=2.4.1.90 2.4.1.90] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1NWG OCA]. |
==Reference== | ==Reference== | ||
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[[Category: N-acetyllactosamine synthase]] | [[Category: N-acetyllactosamine synthase]] | ||
[[Category: Protein complex]] | [[Category: Protein complex]] | ||
| - | [[Category: Qasba, P | + | [[Category: Qasba, P K.]] |
[[Category: Ramakrishnan, B.]] | [[Category: Ramakrishnan, B.]] | ||
| - | [[Category: Shah, P | + | [[Category: Shah, P S.]] |
[[Category: BGN]] | [[Category: BGN]] | ||
[[Category: CA]] | [[Category: CA]] | ||
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[[Category: alpha-lactalbumin; beta1]] | [[Category: alpha-lactalbumin; beta1]] | ||
| - | ''Page seeded by [http:// | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 14:10:49 2008'' |
Revision as of 12:10, 21 February 2008
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BETA-1,4-GALACTOSYLTRANSFERASE COMPLEX WITH ALPHA-LACTALBUMIN AND N-BUTANOYL-GLUCOAMINE
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.
About this Structure
1NWG 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 1JNA. Active as N-acetyllactosamine synthase, with EC number 2.4.1.90 Full crystallographic information is available from OCA.
Reference
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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