1tw5

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spinqualitylabelsall models 1tw5, resolution 2.30Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

beta1,4-galactosyltransferase mutant M344H-Gal-T1 in complex with Chitobiose

Overview

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.

About this Structure

1TW5 is a Single protein structure of sequence from Bos taurus with CBS, MN, SO4, UDH, MES and DIO as ligands. Full crystallographic information is available from OCA.

Reference

Effect of the Met344His mutation on the conformational dynamics of bovine beta-1,4-galactosyltransferase: crystal structure of the Met344His mutant in complex with chitobiose., Ramakrishnan B, Boeggeman E, Qasba PK, Biochemistry. 2004 Oct 5;43(39):12513-22. PMID:15449940

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