The Ohio State Biochemistry Program, Center for RNA Biology, and Department of Chemistry and Biochemistry , The Ohio State University , Columbus , Ohio 43210 , United States.
Biochemistry. 2019 Feb 5;58(5):336-345. doi: 10.1021/acs.biochem.8b01047. Epub 2018 Dec 3.
The SPOUT family of enzymes makes up the second largest of seven structurally distinct groups of methyltransferases and is named after two evolutionarily related RNA methyltransferases, SpoU and TrmD. A deep trefoil knotted domain in the tertiary structures of member enzymes defines the SPOUT family. For many years, formation of a homodimeric quaternary structure was thought to be a strict requirement for all SPOUT enzymes, critical for substrate binding and formation of the active site. However, recent structural characterization of two SPOUT members, Trm10 and Sfm1, revealed that they function as monomers without the requirement of this critical dimerization. This unusual monomeric form implies that these enzymes must exhibit a nontraditional substrate binding mode and active site architecture and may represent a new division in the SPOUT family with distinct properties removed from the dimeric enzymes. Here we discuss the mechanistic features of SPOUT enzymes with an emphasis on the monomeric members and implications of this "novel" monomeric structure on cofactor and substrate binding.
SPOUT 酶家族由七个结构上不同的甲基转移酶家族中的第二大组成，以两个进化上相关的 RNA 甲基转移酶 SpoU 和 TrmD 命名。成员酶的三级结构中的深三叶形纽结域定义了 SPOUT 家族。多年来，形成同源二聚体四级结构被认为是所有 SPOUT 酶的严格要求，这对于底物结合和活性位点的形成至关重要。然而，最近对两个 SPOUT 成员 Trm10 和 Sfm1 的结构特征分析表明，它们以单体形式发挥作用，而不需要这种关键的二聚化。这种不寻常的单体形式表明，这些酶必须表现出非传统的底物结合模式和活性位点结构，并且可能代表 SPOUT 家族的一个新分支，其特性与二聚体酶不同。本文将重点讨论 SPOUT 酶的机制特征，并讨论这种“新颖”的单体结构对辅因子和底物结合的影响。
