Vrielink A, Rüger W, Driessen H P, Freemont P S
Protein Structure Laboratory, Imperial Cancer Research Fund, London.
EMBO J. 1994 Aug 1;13(15):3413-22. doi: 10.1002/j.1460-2075.1994.tb06646.x.
Bacteriophage T4 beta-glucosyltransferase (EC 2.4.1.27) catalyses the transfer of glucose from uridine diphosphoglucose to hydroxymethyl groups of modified cytosine bases in T4 duplex DNA forming beta-glycosidic linkages. The enzyme forms part of a phage DNA protection system. We have solved and refined the crystal structure of recombinant beta-glucosyltransferase to 2.2 A resolution in the presence and absence of the substrate, uridine diphosphoglucose. The structure comprises two domains of similar topology, each reminiscent of a nucleotide binding fold. The two domains are separated by a central cleft which generates a concave surface along one side of the molecule. The substrate-bound complex reveals only clear electron density for the uridine diphosphate portion of the substrate. The UDPG is bound in a pocket at the bottom of the cleft between the two domains and makes extensive hydrogen bonding contacts with residues of the C-terminal domain only. The domains undergo a rigid body conformational change causing the structure to adopt a more closed conformation upon ligand binding. The movement of the domains is facilitated by a hinge region between residues 166 and 172. Electrostatic surface potential calculations reveal a large positive potential along the concave surface of the structure, suggesting a possible site for duplex DNA interaction.
噬菌体T4β-葡萄糖基转移酶（EC 2.4.1.27）催化尿苷二磷酸葡萄糖中的葡萄糖转移至T4双链DNA中修饰胞嘧啶碱基的羟甲基上，形成β-糖苷键。该酶是噬菌体DNA保护系统的一部分。我们已解析并精修了重组β-葡萄糖基转移酶在有和没有底物尿苷二磷酸葡萄糖存在时的晶体结构，分辨率达到2.2埃。该结构由两个拓扑结构相似的结构域组成，每个结构域都让人联想到核苷酸结合折叠。这两个结构域由一个中央裂隙隔开，该裂隙在分子的一侧形成一个凹面。底物结合复合物仅显示底物尿苷二磷酸部分清晰的电子密度。UDPG结合在两个结构域之间裂隙底部的一个口袋中，并且仅与C末端结构域的残基形成广泛的氢键接触。这些结构域发生刚体构象变化，导致结构在配体结合时采取更封闭的构象。结构域的移动由166和172位残基之间的一个铰链区促进。静电表面电势计算显示沿该结构凹面有很大的正电势，表明这可能是双链DNA相互作用的位点。
