Aminocarboxypropyl (acp) modified nucleotides in RNA: enzymes, structures and functions

m1acp3 - 1191（S.酿酒酵母）的超修饰是独特的，并推测存在于所有真核生物的18 S rRNA中。在SPP的第一个阶段，我们功能和结构特征Tsr 3-转移acp基团的酶，在最后一步在这个高度修饰的核苷酸的生物合成过程中的m1腺苷酸。我们解决了在SAM结合和载脂蛋白状态下Tsr 3的古细菌同系物的X射线结构。令人惊讶的是，Tsr 3显示出与SPOUT类RNA甲基转移酶相同的折叠，但具有独特的SAM结合模式，支持SAM的acp基团转移到其RNA底物。DTW序列动机是该SAM结合位点的整体结构部分。这些结构上的见解和序列的相似性为acp转移酶的鉴定开辟了一条新的途径。具有预测DTW动机的蛋白质广泛存在于生命的各个领域。大肠我们目前的数据表明，DTW蛋白YfiP催化tRNA中的acp 3U-47修饰，但仅当m7 G-46修饰也存在时才有效。此外，在高等真核生物中，存在tRNA acp转移酶的几种同系物，其中一些可能特异性地修饰来自不同细胞器的tRNA。将研究acp修饰对tRNA的功能重要性。我们还将描绘这种酶类的tRNA识别的结构基础，并将其与Tsr 3蛋白与其核糖体RNA底物的可能不同的结合模式进行比较。

The m1acp3Ѱ1191 (S. cerevisiae) hypermodification is unique and presumably present in the 18S rRNAs of all eukaryotes. During the first period of the SPP we functionally and structurally characterized Tsr3 - the enzyme transferring an acp group to m1Ѱ during the last step in the biosynthesis of this hypermodified nucleotide. We solved X-ray structures of archaeal homologs of Tsr3 in the SAM-bound and the apo state. Surprisingly, Tsr3 showed the same fold similar as SPOUT-class RNA methyltransferases but a unique SAM-binding mode that supports the transfer of the acp group of SAM to its RNA substrate. A DTW sequence motive is an integral structural part of this SAM-binding site. These structural insights and sequence similarities opened a new access for the identification of acp transferases. Proteins with predicted DTW motives are widespread in all domains of life. For E. coli our current data suggest that the DTW protein YfiP catalyzes the acp3U-47 modification in tRNAs but is only efficient when an m7G-46 modification is also present. Furthermore, in higher eukaryotes several homologs of tRNA acp transferases are present, some of which possibly modify specifically tRNAs from different organelles. The functional importance of acp modification for tRNAs will be investigated. We also will delineate the structural basis for tRNA recognition of this enzyme class and compare it with the probably different binding mode of Tsr3 proteins to their ribosomal RNA substrates.