1c3j
From Proteopedia
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T4 PHAGE BETA-GLUCOSYLTRANSFERASE: SUBSTRATE BINDING AND PROPOSED CATALYTIC MECHANISM
Overview
beta-Glucosyltransferase (BGT) is a DNA-modifying enzyme encoded by, bacteriophage T4 which catalyses the transfer of glucose (Glc) from, uridine diphosphoglucose (UDP-Glc) to 5-hydroxymethylcytosine (5-HMC) in, double-stranded DNA. The glucosylation of T4 phage DNA is part of a phage, DNA protection system aimed at host nucleases. We previously reported the, first three-dimensional structure of BGT determined from crystals grown in, ammonium sulphate containing UDP-Glc. In this previous structure, we did, not observe electron density for the Glc moiety of UDP-Glc nor for two, large surface loop regions (residues 68-76 and 109-122). Here we report, two further BGT co-crystal structures, in the presence of UDP product, (form I) and donor substrate UDP-Glc (form II), respectively. Form I, crystals are grown in ammonium sulphate and the structure has been, determined to 1.88 A resolution (R -factor 19.1 %). Form II crystals are, grown in polyethyleneglycol 4000 and the structure has been solved to 2.3, A resolution (R -factor 19.8 %). The form I structure is isomorphous to, our previous BGT UDP-Glc structure. The form II structure, however, has, allowed us to model the two missing surface loop regions and thus provides, the first complete structural description of BGT. In this low-salt crystal, form, we see no electron density for the Glc moiety from UDP-Glc similar, to previous observations. Biochemical data however, shows that BGT can, cleave UDP-Glc in the absence of DNA acceptor, which probably accounts for, the absence of Glc in our UDP-Glc substrate structures. The complete BGT, structure now provides a basis for detailed modelling of a BGT HMC-DNA, ternary complex. By using the structural similarity between the catalytic, core of glycogen phosphorylase (GP) and BGT, we have modelled the position, of the Glc moiety in UDP-Glc. From these two models, we propose a, catalytic mechanism for BGT and identify residues involved in both DNA, binding and in stabilizing a "flipped-out" 5-HMC nucleotide.
About this Structure
1C3J is a Single protein structure of sequence from Bacteriophage t4 with UDP as ligand. Active as DNA beta-glucosyltransferase, with EC number 2.4.1.27 Full crystallographic information is available from OCA.
Reference
T4 phage beta-glucosyltransferase: substrate binding and proposed catalytic mechanism., Morera S, Imberty A, Aschke-Sonnenborn U, Ruger W, Freemont PS, J Mol Biol. 1999 Sep 24;292(3):717-30. PMID:10497034
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