Elkins Patricia A, Watts Joseph M, Zalacain Magdalena, van Thiel Adam, Vitazka Patrik R, Redlak Maria, Andraos-Selim Cecile, Rastinejad Fraydoon, Holmes Walter M
GlaxoSmithKline, 709 Swedeland Road, UE0447, King of Prussia, PA 19406, USA.
J Mol Biol. 2003 Nov 7;333(5):931-49. doi: 10.1016/j.jmb.2003.09.011.
The crystal structure of Escherichia coli tRNA (guanosine-1) methyltransferase (TrmD) complexed with S-adenosyl homocysteine (AdoHcy) has been determined at 2.5A resolution. TrmD, which methylates G37 of tRNAs containing the sequence G36pG37, is a homo-dimer. Each monomer consists of a C-terminal domain connected by a flexible linker to an N-terminal AdoMet-binding domain. The two bound AdoHcy moieties are buried at the bottom of deep clefts. The dimer structure appears integral to the formation of the catalytic center of the enzyme and this arrangement strongly suggests that the anticodon loop of tRNA fits into one of these clefts for methyl transfer to occur. In addition, adjacent hydrophobic sites in the cleft delineate a defined pocket, which may accommodate the GpG sequence during catalysis. The dimer contains two deep trefoil peptide knots and a peptide loop extending from each knot embraces the AdoHcy adenine ring. Mutational analyses demonstrate that the knot is important for AdoMet binding and catalytic activity, and that the C-terminal domain is not only required for tRNA binding but plays a functional role in catalytic activity.
已确定大肠杆菌tRNA（鸟苷-1）甲基转移酶（TrmD）与S-腺苷同型半胱氨酸（AdoHcy）复合物的晶体结构，分辨率为2.5埃。TrmD可使含有G36pG37序列的tRNA的G37甲基化，它是一种同型二聚体。每个单体由一个通过柔性接头连接到N端腺苷甲硫氨酸结合结构域的C端结构域组成。两个结合的AdoHcy部分埋在深裂隙的底部。二聚体结构似乎是酶催化中心形成所必需的，这种排列强烈表明tRNA的反密码子环适合进入这些裂隙之一以进行甲基转移。此外，裂隙中相邻的疏水位点界定了一个特定的口袋，在催化过程中可能容纳GpG序列。二聚体包含两个深的三叶肽结，并且从每个结延伸的肽环环绕着AdoHcy腺嘌呤环。突变分析表明，该结对于腺苷甲硫氨酸结合和催化活性很重要，并且C端结构域不仅是tRNA结合所必需的，而且在催化活性中起功能作用。
