Larivière Laurent, Moréra Solange
Laboratoire d'Enzymologie et Biochimie Structurales, UPR 9063 CNRS, Bât. 34, 1 Avenue de la Terrasse, 91198, Gif-sur-Yvette, France
J Mol Biol. 2002 Nov 29;324(3):483-90. doi: 10.1016/s0022-2836(02)01091-4.
T4 phage beta-glucosyltransferase (BGT) modifies T4 DNA. We crystallized BGT with UDP-glucose and a 13mer DNA fragment containing an abasic site. We obtained two crystal structures of a ternary complex BGT-UDP-DNA at 1.8A and 2.5A resolution, one with a Tris molecule and the other with a metal ion at the active site. Both structures reveal a large distortion in the bound DNA. BGT flips the deoxyribose moiety at the abasic site to an extra-helical position and induces a 40 degrees bend in the DNA with a marked widening of the major groove. The Tris molecule mimics the glucose moiety in its transition state. The base-flipping mechanism, which has so far been observed only for glycosylases, methyltransferases and endonucleases, is now reported for a glucosyltransferase. BGT is unique in binding and inserting a loop into the DNA duplex through the major groove only. Furthermore, BGT compresses the backbone DNA one base further than the target base on the 3'-side.
T4噬菌体β-葡萄糖基转移酶（BGT）可修饰T4 DNA。我们将BGT与UDP-葡萄糖以及一个含有无碱基位点的13聚体DNA片段进行了结晶。我们获得了三元复合物BGT-UDP-DNA在1.8埃和2.5埃分辨率下的两种晶体结构，一种在活性位点含有一个Tris分子，另一种含有一个金属离子。两种结构均显示结合的DNA存在较大扭曲。BGT将无碱基位点处的脱氧核糖部分翻转至螺旋外位置，并使DNA产生40度弯曲，同时大沟明显变宽。Tris分子在其过渡态模拟葡萄糖部分。碱基翻转机制迄今仅在糖基化酶、甲基转移酶和核酸内切酶中观察到，现在报道在一种葡萄糖基转移酶中也存在。BGT的独特之处在于仅通过大沟与DNA双链结合并插入一个环。此外，BGT在3'侧比目标碱基进一步压缩主链DNA一个碱基。
