Zegers Ingrid, Gigot Daniel, van Vliet Françoise, Tricot Catherine, Aymerich Stéphane, Bujnicki Janusz M, Kosinski Jan, Droogmans Louis
Laboratorium Ultrastructuur, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussel, Belgium.
Nucleic Acids Res. 2006 Apr 5;34(6):1925-34. doi: 10.1093/nar/gkl116. Print 2006.
The structure of Bacillus subtilis TrmB (BsTrmB), the tRNA (m7G46) methyltransferase, was determined at a resolution of 2.1 A. This is the first structure of a member of the TrmB family to be determined by X-ray crystallography. It reveals a unique variant of the Rossmann-fold methyltransferase (RFM) structure, with the N-terminal helix folded on the opposite site of the catalytic domain. The architecture of the active site and a computational docking model of BsTrmB in complex with the methyl group donor S-adenosyl-L-methionine and the tRNA substrate provide an explanation for results from mutagenesis studies of an orthologous enzyme from Escherichia coli (EcTrmB). However, unlike EcTrmB, BsTrmB is shown here to be dimeric both in the crystal and in solution. The dimer interface has a hydrophobic core and buries a potassium ion and five water molecules. The evolutionary analysis of the putative interface residues in the TrmB family suggests that homodimerization may be a specific feature of TrmBs from Bacilli, which may represent an early stage of evolution to an obligatory dimer.
已确定枯草芽孢杆菌TrmB（BsTrmB）——tRNA（m7G46）甲基转移酶的结构，分辨率为2.1埃。这是通过X射线晶体学确定的TrmB家族成员的首个结构。它揭示了罗斯曼折叠甲基转移酶（RFM）结构的一种独特变体，其N端螺旋折叠在催化结构域的相反位置。活性位点的结构以及BsTrmB与甲基供体S-腺苷-L-甲硫氨酸和tRNA底物复合物的计算对接模型，为来自大肠杆菌的同源酶（EcTrmB）的诱变研究结果提供了解释。然而，与EcTrmB不同，此处显示BsTrmB在晶体和溶液中均为二聚体。二聚体界面有一个疏水核心，并包埋一个钾离子和五个水分子。对TrmB家族假定界面残基的进化分析表明，同型二聚化可能是芽孢杆菌属TrmB的一个特定特征，这可能代表了向 obligatory dimer进化的早期阶段。
