Biology subjects

Tengo, L.

Publications and source records attributed to Tengo, L..

3 recordsLinked to original sources

bioRxiv2024

Structural basis of Spliced Leader RNA recognition by the Trypanosoma brucei cap-binding complex

Kinetoplastids are a clade of eukaryotic protozoans that include human parasitic pathogens like trypanosomes and Leishmania species. In these organisms, protein-coding genes are transcribed as polycistronic pre-mRNAs, which need to be processed by the coupled action of trans-splicing and polyadenylation to yield monogenic mature mRNAs. During trans-splicing, a universal RNA sequence, the spliced leader RNA (SL RNA) mini-exon, is added to the 5-end of each mRNA. The 5-end of this mini-exon carries a hypermethylated cap structure and is bound by a trypanosomatid-specific cap-binding complex (CBC). The function of three of the kinetoplastid CBC subunits is unknown, but an essential role in cap binding and trans-splicing has been suggested. Here, we report cryo-EM structures that reveal the molecular architecture of the Trypanosoma brucei CBC (TbCBC) complex. We find that TbCBC interacts with two distinct features of the SL RNA. The TbCBP20 subunit interacts with the m7G cap while TbCBP66 recognizes double-stranded portions of the SL RNA. Our findings pave the way for future research on mRNA maturation in kinetoplastids. Moreover, the observed structural similarities and differences between TbCBC and the mammalian cap-binding complex will be crucial for considering the potential of TbCBC as a target for anti-trypanosomatid drug development. HighlightsO_LICryo-EM reveals the molecular architecture of the tetrameric Trypanosoma brucei cap-binding complex (TbCBC). C_LIO_LITbCBP110 is the kinetoplastid homolog of mammalian CBP80 and forms the scaffold for TbCBP20. C_LIO_LITbCBC has a bilobal architecture with TbCBP30 bridging the flexibly attached TbCBP66 subunit and the TbCBP20-TbCBP110 core complex. C_LIO_LITbCBC recognizes the m7G RNA cap independent of the other trypanosomatid-specific cap4 methylations. C_LIO_LIThe TbCBP66 subunit contains a binding site for dsRNA, augmenting the affinity of TbCBC for the SL RNA. C_LI

molecular biology↗

bioRxiv2023

Structural basis of tRNA recognition by the m3C-RNA-methyltransferase METTL6 in complex with SerRS seryl-tRNA synthetase

Methylation of cytosine 32 in the anticodon loop of tRNAs to 3-methylcytosine (m3C) is crucial for cellular translation fidelity 1. Misregulation of the RNA methyltransferases setting this modification can cause aggressive cancers and metabolic disturbances 2,3. However, our understanding of the substrate selection and catalysis mode of the m3C RNA methyltransferases is currently still lacking. Here, we report the cryo-electron microscopy structure of the m3C tRNA methyltransferase METTL6 in complex with seryl-tRNA synthetase (SerRS) and their common substrate tRNASer. Through the complex structure, we identify the tRNA binding domain of METTL6. We show that SerRS acts as the tRNASer substrate selection factor for METTL6. We reveal how METTL6 and SerRS jointly coordinate the long variable arm of tRNASer in their interface. We demonstrate that SerRS augments the methylation activity of METTL6 and that direct contacts between METTL6 and SerRS are necessary for efficient tRNASer methylation. Finally, based on the structure of METTL6 in complex with SerRS and tRNASer, we postulate a universal tRNA binding mode for m3C RNA methyltransferases including METTL2 and METTL8, suggesting that these mammalian paralogues use similar ways to engage their respective tRNA substrates and co-factors.

molecular biology↗

bioRxiv2022

Sequence-independent substrate selection by the eukaryotic wobble base deaminase ADAT2/3 involves multiple protein domains and distortion of the tRNA anticodon loop

The essential deamination of adenosine A34 to inosine at the wobble base is the individual tRNA modification with the greatest effects on mRNA decoding, empowering a single tRNA to translate three different codons. To date, many aspects of how eukaryotic deaminases specifically select their multiple substrates remain unclear. Here, using cryo-EM, we present the first structure of a eukaryotic ADAT2/3 deaminase bound to a full-length tRNA, revealing that the enzyme distorts the anticodon loop, but in contrast to the bacterial enzymes, selects its substrate via sequence-independent contacts of eukaryote-acquired flexible or intrinsically unfolded motifs distal from the conserved catalytic core. A novel gating mechanism for substrate entry to the active site is identified. Our multi-step tRNA recognition model yields insights into how RNA editing by A34 deamination evolved, shaped the genetic code, and directly impacts the eukaryotic proteome.

molecular biology↗