{'fraction_non_alphanumeric': 0.02957807742496738, 'fraction_numerical': 0.02957807742496738, 'mean_word_length': 5.3535911602209945, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Crystal structure of Thermotoga maritima SPOUT superfamily RNA methyltransferase Tm1570 in complex with S‐adenosyl‐L‐methionine

RNAs involved in translation and post-transcriptional processing contain a large number of modified nucleosides.1 In tRNAs, over 80 different modifications have been observed,2 and many of these modifications are important for tRNA function. Modifications within the anticodon loop are necessary for proper codon recognition,3 while those in the Dand T-loops facilitate folding and stabilization of the tRNA.4 Ribosomal RNA modifications are clustered around the catalytic center and other crucial regions of the ribosome, further underscoring their importance in translation.5 The ‘‘SPOUT’’ [SpoU-TrmD] superfamily methyltransferases (MTases) are a large class of S-adenosyl-L-methionine (AdoMet)-dependent RNA MTases that exhibit a Rossmannoid a/b-fold with a deep trefoil knot.6 Several members of the SPOUT superfamily have been characterized functionally7 and they have been found to be involved in post-transcriptional RNA modification by catalyzing methylation of the 20-OH group of ribose,8–10 the N-1 atom of guanosine 37 in tRNA,11,12 or the N-3 atom of uridine 1498 in 16S rRNA.13 Despite a wealth of sequence data on the SPOUT superfamily MTases in the database, structural data are limited to only a few COGs (Clusters of Orthologous Groups) of the SPOUT superfamily.7 Therefore, further structural characterization of the SPOUT superfamily members are required. Thermotoga maritima Tm1570 is a member of the SPOUT MTase superfamily,7 belonging to the COG4752 family, which comprises a few bacterial proteins with erratic phyletic distribution, mostly from extremophiles (e.g., T. maritima and Synthropus acidotrophicus) but also from pathogens such as Fusibacterium nucleatum.7 COG4752 also has been dubbed SpoU family, implying a functional link with 20-O-ribose MTases.14 However, the molecular function of Tm1570 remains to be established. In this study, we have solved the crystal structure of the T. maritima Tm1570 MTase in complex with AdoMet at 2.00 Å resolution. This work represents the first crystal structure of a member of the COG4752 family, thus contributing to expand our knowledge on the structural features of the SPOUT MTase superfamily.