High resolution crystal structures of T4 phage beta-glucosyltransferase: Induced fit and effect of substrate and metal binding

beta -Glucosyltransferase (BGT) is a DNA-modifying enzyme encoded by bacter iophage T4 that transfers glucose from uridine diphosphoglucose to 5-hydrox ymethyl cytosine bases of phage T4 DNA. We report six X-ray structures of t he substrate-free and the UDP-bound enzyme. Four also contain metal ions wh ich activate the enzyme, including Mg2+ in forms I and 2 and Mn2+ or Ca2+. The substrate-free BGT structure differs by a domain movement from one prev iously determined in another space group. Further domain movements are seen in the complex with UDP and the four UDP-metal complexes. Mg2+, Mn2+ and C a2+ bind near the beta -phosphate of the nucleotide, but they occupy slight ly different positions and have different ligands depending on the metal an d the crystal form. Whilst the metal site observed in these complexes with the product UDP is not compatible with a role in activating glucose transfe r, it approximates the position of the positive charge in the oxocarbonium ion thought to form on the glucose moiety of the substrate during catalysis . (C) 2001 Academic Press.