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| {{STRUCTURE_1tw1| PDB=1tw1 | SCENE= }} | | {{STRUCTURE_1tw1| PDB=1tw1 | SCENE= }} |
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| '''beta-1,4-galactosyltransferase mutant Met344His (m344H-Gal-T1) complex with UDP-galactose and magnesium'''
| | ===beta-1,4-galactosyltransferase mutant Met344His (m344H-Gal-T1) complex with UDP-galactose and magnesium=== |
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| ==Overview==
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| Beta-1,4-galactosyltransferase (beta4Gal-T1) in the presence of manganese ion transfers galactose from UDP-galactose (UDP-Gal) to N-acetylglucosamine (GlcNAc) that is either free or linked to an oligosaccharide. Crystallographic studies on bovine beta4Gal-T1 have shown that the primary metal binding site is located in the hinge region of a long flexible loop, which upon Mn(2+) and UDP-Gal binding changes from an open to a closed conformation. This conformational change creates an oligosaccharide binding site in the enzyme. Neither UDP nor UDP analogues efficiently induce these conformational changes in the wild-type enzyme, thereby restricting the structural analysis of the acceptor binding site. The binding of Mn(2+) involves an uncommon coordination to the Sdelta atom of Met344; when it is mutated to His, the mutant M344H, in the presence of Mn(2+) and UDP-hexanolamine, readily changes to a closed conformation, facilitating the structural analysis of the enzyme bound with an oligosaccharide acceptor. Although the mutant M344H loses 98% of its Mn(2+)-dependent activity, it exhibits 25% of its activity in the presence of Mg(2+). The crystal structures of M344H-Gal-T1 in complex with either UDP-Gal.Mn(2+) or UDP-Gal.Mg(2+), determined at 2.3 A resolution, show that the mutant enzyme in these complexes is in a closed conformation, and the coordination stereochemistry of Mg(2+) is quite similar to that of Mn(2+). Although either Mn(2+) or Mg(2+), together with UDP-Gal, binds and changes the conformation of the M344H mutant to the closed one, it is the Mg(2+) complex that engages efficiently in catalyses. Thus, this property enabled us to crystallize the M344H mutant for the first time with the acceptor substrate chitobiose in the presence of UDP-hexanolamine and Mn(2+). The crystal structure determined at 2.3 A resolution reveals that the GlcNAc residue at the nonreducing end of chitobiose makes extensive hydrophobic interactions with the highly conserved Tyr286 residue.
| | The line below this paragraph, {{ABSTRACT_PUBMED_15449940}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 15449940 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_15449940}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Met344his mutation]] | | [[Category: Met344his mutation]] |
| [[Category: Mn binding]] | | [[Category: Mn binding]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 10:26:23 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Tue Jul 29 08:03:43 2008'' |
