This preprint presents the first structural insights into a non-canonical complex between human Dicer (hDicer) and tRNA. Using an integrated structural biology approach, the authors report that hDicer can directly engage tRNA substrates in conformations distinct from canonical Dicer substrates (such as pre-miRNAs). The work reframes tRNAs not only as translation components but also as direct substrates for hDicer, capable of producing tRNA-derived small RNAs (tsRNAs) that participate in regulatory pathways.
The abstract describes visualization of the complex and interpretation of RNA conformation and dynamics, but detailed structural parameters (for example, cryo-EM resolution, atomic coordinates, or specific contact residues) are not reported in the abstract itself and therefore are not reproduced here.
The authors combined three complementary techniques to interrogate the hDicer–tRNA interaction:
cryo-electron microscopy (cryo-EM) to obtain structural snapshots of the complex,
selective 2′-hydroxyl acylation analyzed by primer extension (SHAPE) to probe RNA flexibility and conformation in solution,
molecular dynamics (MD) simulations to model conformational dynamics and refine understanding of the interaction.
This multimodal strategy links static structural data with solution-state chemistry and computational dynamics, enabling the authors to propose mechanistic models for recognition and cleavage. Specific experimental conditions, map statistics, or SHAPE reactivity profiles are not provided in the source abstract, so those methodological details are not summarized here.
A central finding reported is that tRNAs adopt alternative conformations that are recognized and processed by hDicer. Rather than requiring canonical Dicer substrates (such as hairpin-like pre-miRNAs), hDicer can engage tRNAs in non-canonical structural states, enabling cleavage that produces tsRNAs. The combination of cryo-EM and SHAPE data supports the existence of these alternative folds or local structural rearrangements that facilitate hDicer binding.
By demonstrating recognition of alternative tRNA conformers, the study expands the known substrate specificity of human Dicer and suggests structural plasticity in both enzyme and RNA that underlies non-canonical processing events.
The authors report a functional link between tRNA chemical modification and cleavage by hDicer: cleavage is facilitated by 5-methylcytosine (m5C), a modification deposited by the methyltransferase NSUN2. This observation supports a model in which RNA modification state influences susceptibility to Dicer-mediated processing, establishing a modification-dependent pathway for tsRNA biogenesis.
The abstract does not include quantitative measures of how m5C affects cleavage efficiency, nor does it provide detailed mapping of modified sites relative to cleavage positions; those experimental specifics are not reported in the source abstract and therefore are not recapitulated here.
tsRNAs produced by hDicer have been implicated in nuclear gene silencing and in regulation of numerous disease-associated genes. By establishing that hDicer can generate tsRNAs from tRNAs in a modification-dependent manner, the work redefines the origins of a class of small RNAs with regulatory potential. The findings imply that tRNA modification enzymes such as NSUN2 can indirectly shape small RNA populations and downstream gene regulatory networks by modulating substrate availability or cleavage susceptibility.
This model places tRNA biology and RNA modification at the intersection of small RNA biogenesis and gene regulation, with potential relevance to diseases linked to tsRNA function or to perturbations in tRNA modification pathways.
This article is posted as a preprint on bioRxiv and has not been peer reviewed. The abstract provides high-level findings and methodological summary, but specific structural metrics, experimental parameters, and quantitative data are not reported in the abstract and are therefore not included here. The authors declare no competing interests. Funding acknowledgement in the source identifies the Medical Research Council as a declared funder.
Readers should consult the full preprint and associated supplementary material for detailed methods, data, and validation prior to clinical or translational interpretation. The structural and mechanistic claims summarized here reflect the content of the bioRxiv abstract and associated metadata only.