McCarthy Andrew A, Biget Laurent, Lin Chenwei, Petiard Vincent, Tanksley Steve D, McCarthy James G
European Molecular Biology Laboratory, 6 Rue Jules Horowitz, BP 181, 38042 Grenoble, France.
Acta Crystallogr Sect F Struct Biol Cryst Commun. 2007 Apr 1;63(Pt 4):304-7. doi: 10.1107/S1744309107009268. Epub 2007 Mar 12.
Caffeine is a secondary metabolite produced by a variety of plants including Coffea canephora (robusta) and there is growing evidence that caffeine is part of a chemical defence strategy protecting young leaves and seeds from potential predators. The genes encoding XMT and DXMT, the enzymes from Coffea canephora (robusta) that catalyse the three independent N-methyl transfer reactions in the caffeine-biosynthesis pathway, have been cloned and the proteins have been expressed in Escherichia coli. Both proteins have been crystallized in the presence of the demethylated cofactor S-adenosyl-L-cysteine (SAH) and substrate (xanthosine for XMT and theobromine for DXMT). The crystals are orthorhombic, with space group P2(1)2(1)2(1) for XMT and C222(1) for DXMT. X-ray diffraction to 2.8 A for XMT and to 2.5 A for DXMT have been collected on beamline ID23-1 at the ESRF.
咖啡因是包括卡内弗拉咖啡（罗布斯塔咖啡）在内的多种植物产生的次生代谢产物，越来越多的证据表明，咖啡因是化学防御策略的一部分，可保护幼叶和种子免受潜在捕食者的侵害。编码XMT和DXMT的基因已被克隆，这两种酶来自卡内弗拉咖啡（罗布斯塔咖啡），可催化咖啡因生物合成途径中的三个独立的N-甲基转移反应，并且其蛋白质已在大肠杆菌中表达。两种蛋白质均在去甲基化辅因子S-腺苷-L-半胱氨酸（SAH）和底物（XMT的底物为黄嘌呤核苷，DXMT的底物为可可碱）存在的情况下结晶。晶体为正交晶系，XMT的空间群为P2(1)2(1)2(1)，DXMT的空间群为C222(1)。在欧洲同步辐射装置的ID23-1光束线上，已收集到XMT在2.8埃、DXMT在2.5埃的X射线衍射数据。
