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1oqm

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[[Image:1oqm.gif|left|200px]]
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[[Image:1oqm.png|left|200px]]
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{{STRUCTURE_1oqm| PDB=1oqm | SCENE= }}
{{STRUCTURE_1oqm| PDB=1oqm | SCENE= }}
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'''A 1:1 complex between alpha-lactalbumin and beta1,4-galactosyltransferase in the presence of UDP-N-acetyl-galactosamine'''
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===A 1:1 complex between alpha-lactalbumin and beta1,4-galactosyltransferase in the presence of UDP-N-acetyl-galactosamine===
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==Overview==
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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.
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(as it appears on PubMed at http://www.pubmed.gov), where 11916963 is the PubMed ID number.
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{{ABSTRACT_PUBMED_11916963}}
==About this Structure==
==About this Structure==
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[[Category: Beta1,4-galactosyltransferase]]
[[Category: Beta1,4-galactosyltransferase]]
[[Category: Udp-galnac]]
[[Category: Udp-galnac]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 04:09:53 2008''
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Tue Jul 29 07:35:55 2008''

Revision as of 04:36, 29 July 2008

Image:1oqm.png

Template:STRUCTURE 1oqm

A 1:1 complex between alpha-lactalbumin and beta1,4-galactosyltransferase in the presence of UDP-N-acetyl-galactosamine

Template:ABSTRACT PUBMED 11916963

About this Structure

1OQM is a Protein complex structure of sequences from Bos taurus and Mus musculus. This structure supersedes the now removed PDB entry 1l7w. Full crystallographic information is available from OCA.

Reference

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

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