RNA molecules, composed of the ribonucleotides adenine (A), uracil (U), guanine (G), and cytosine (C), are central to cellular function, conveying genetic information and regulating gene expression. Among these molecules, miRNAs are short regulatory RNAs integral to the RNA-induced silencing complex (RISC), modulating gene expression by guiding the silencing machinery to specific messenger RNA targets. DICER’s role is to cleave precursor double-stranded RNAs into these active miRNA fragments, a process that demands both specificity and precision to maintain cellular homeostasis.

Despite the fundamental nature of DICER in RNA silencing pathways, the precise molecular determinants enabling its striking accuracy had remained elusive. Through a combination of advanced biochemical assays and high-resolution cryogenic electron microscopy (cryo-EM), the HKUST team—led by Professor Tuan Anh Nguyen and his PhD students Minh Khoa Ngo and Cong Truc Le—captured atomic-level snapshots of DICER engaged with various RNA substrates. These structural insights unveil the enzyme’s dynamic conformational shifts prior to cleavage, illustrating how DICER meticulously aligns RNA molecules within its catalytic core.

Central to this process are two distinct 5′-end binding pockets within the enzyme’s structure, each demonstrating a nucleotide preference that influences cleavage positioning. Previously recognized was a pocket favoring uracil (U) at the RNA’s 5′-end, guiding the enzyme’s cutting action. Remarkably, the HKUST team identified a second, guanine (G)-preferring pocket, which together with the U-favored site forms a dual-pocket framework. This dual recognition system enables DICER to discern subtle sequence variations, thereby refining the cleavage site selection to single-nucleotide accuracy.

The discovery of this dual-pocket mechanism fundamentally reshapes our understanding of how DICER accommodates diverse RNA sequences, providing a molecular basis for how the enzyme maintains cleavage fidelity across a spectrum of substrates. By modulating the interaction between RNA 5′-end identity and DICER’s structural elements, the enzyme can “read” the RNA code, ensuring that genetic messages are processed correctly and efficiently. This nuanced control is crucial, given that miscleavage can lead to aberrant gene regulation with potentially deleterious biological consequences.

Moreover, the conformational plasticity observed in the cryo-EM structures suggests that DICER undergoes a series of dynamic adjustments to engage its RNA substrates optimally. These rearrangements position RNA strands precisely within the enzyme’s catalytic pocket before cleavage, underscoring a highly orchestrated interplay between protein domains and RNA elements. This interplay highlights an evolved molecular sophistication enabling robust and reliable gene regulatory outcomes.

Beyond broadening our molecular understanding, these insights carry significant translational potential. By elucidating the detailed mechanisms underlying DICER function, this research paves the way for improved RNA-based therapeutics. Precise manipulation of DICER activity could enhance gene silencing technologies, which are increasingly employed in treating genetic disorders and cancers. Furthermore, understanding the structural basis for DICER’s cleavage fidelity informs efforts to diagnose and potentially remediate diseases stemming from dysfunctional RNA processing pathways.

Professor Nguyen emphasized the broader implications of this work, stating that the findings not only illuminate fundamental RNA biology but also establish a platform for novel therapeutic innovations. The dual-pocket recognition model could inspire the design of small molecules or engineered proteins tailored to modulate DICER activity or specificity, offering a route to finely tuned gene regulatory interventions.

The study also addresses long-standing questions about how DICER discriminates among a vast array of RNA substrates differing only subtly in sequence and structure. By integrating 5′-end nucleotide identity, RNA motif recognition, and enzymatic domain movements, DICER exemplifies a molecular machine of remarkable flexibility and precision. These findings highlight the enzyme’s evolved capacity to adapt its activity to diverse regulatory contexts within the cell.

In addition to revealing these mechanistic details, the research underscores the power of combining biochemical experimentation with cutting-edge structural biology techniques, such as cryo-EM, to resolve dynamic protein-RNA interactions at near-atomic resolution. This integrative approach sets a precedent for future studies of RNA-processing enzymes and other nucleic acid-binding proteins.

The HKUST team’s findings mark a significant advance in the field of RNA biology, shedding new light on the molecular choreography that orchestrates gene silencing pathways. By defining the structural basis for DICER’s precision, the study opens avenues for both fundamental biological research and the development of next-generation RNA therapeutics aimed at correcting aberrant gene expression profiles implicated in human disease.

Subject of Research: Cells

Article Title: DICER cleavage fidelity is governed by 5′-end binding pockets

News Publication Date: 4-Mar-2026

Web References: https://www.nature.com/articles/s41586-026-10211-5

References: 10.1038/s41586-026-10211-5

Image Credits: HKUST

Keywords: Life sciences, RNA silencing, DICER, microRNAs, cryo-EM, gene regulation, molecular biology, RNA therapeutics

DICER is a pivotal RNA-processing enzyme that cleaves double-stranded RNA precursors into small interfering RNAs and microRNAs, which orchestrate gene silencing. Despite its central biological role, how DICER structurally transitions between its apo (unbound) and RNA-bound states has remained enigmatic. The new research, by comparing newly resolved RNA-bound dicing-state structures with previously characterized counterparts, illuminates the conformational dynamics underpinning DICER’s function and specificity.

The study employed high-resolution structural analyses of two RNA-bound DICER complexes, termed DICER–26S-GU and DICER–26S-UG, contrasting them with earlier known models, including the apo-DICER structure and a prior dicing-state configuration. Structural comparisons revealed that DICER does not remain static upon RNA engagement; rather, it undergoes profound conformational rearrangements that likely enhance its catalytic fidelity.

A key finding centers on the remarkable plasticity of two domains: the double-stranded RNA-binding domain (dsRBD) and the PAZ domain. Root-mean-square deviation (RMSD) measurements, a quantitative index of structural displacement, indicated pronounced variability in these regions between the functional states. Such flexibility suggests these domains perform orchestrated movements essential for substrate recognition and cleavage.

While earlier work had documented dsRBD repositioning during DICER’s catalytic cycle, the present study distinctively captures the inward translation of the PAZ domain upon RNA binding. This movement results in a significant compaction of the enzyme architecture, shrinking the overall width from approximately 68.0 Å in the previous dicing state to 57.7–58.8 Å in the new RNA-bound structures. This narrowing hints at a more constricted environment optimized for RNA engagement.

Drilling deeper, the inward shift of the PAZ domain is driven by concerted displacements within its secondary structure elements. Notably, an α-helix spanning residues 968–976, which directly contacts the 3′-end of the RNA, moves inward by approximately 7.6 to 8.1 Å. Adjacent β-sheet segments also readjust by about 5.0 to 5.3 Å. These calculated shifts compress the PAZ domain, potentially influencing RNA conformation near the cleavage site.

The compression and reshaping of the PAZ domain likely induce bending of the terminal nucleotides of the RNA substrate. This subtle RNA distortion may be crucial for precise positioning of the cleavage site within the catalytic center, ensuring high fidelity cuts that underlie effective gene silencing. Such mechanistic insights provide strong evidence that DICER’s structural adaptability is a finely tuned regulatory feature rather than a passive byproduct of substrate binding.

Beyond structural remodeling, these observations illuminate how binding pockets at the RNA 5′-end govern cleavage accuracy. The interplay between PAZ domain motions and RNA end recognition emerges as a fundamental determinant of DICER function, revealing new layers of molecular governance that reconcile enzyme flexibility with stringent specificity.

This research also underscores the broader principle that dynamic domain rearrangements within multi-domain enzymes can serve as allosteric mechanisms that regulate activity. In DICER, the inward compaction triggered by RNA binding exemplifies how local structural tweaks cascade into global conformational readjustments, enabling precise enzymatic execution.

The combination of structural biology techniques in this study, including cryo-electron microscopy and RMSD analyses, sets a new standard for dissecting RNA-protein interactions at near-atomic resolution. These advances empower scientists to map transient and subtle conformational changes that are often challenging to capture, opening avenues for targeted drug design.

Therapeutically, understanding DICER’s conformational states and RNA engagement channels offers promising strategies for modulating RNA interference pathways. Given the central role of microRNAs and siRNAs in diseases ranging from cancer to viral infections, fine-tuning DICER activity could enable novel treatment modalities.

The study’s revelations about the PAZ domain inward motion and associated nucleotide bending also invite future exploration of how mutations or chemical modifications could disrupt this delicate mechanism. Such disruptions may underpin certain pathologies or provide targets for selective inhibitors that modulate RNA processing.

In sum, these findings significantly enrich the conceptual framework around RNA interference enzyme mechanics. By elucidating how DICER structurally adapts to bind and process RNA substrates with high fidelity, the research deepens our understanding of gene regulatory machinery and opens the door to innovative biotechnological and medical applications.

As the field advances, integrating these structural insights with cellular and biochemical data will be pivotal for translating molecular knowledge into functional outcomes. The dynamic dance of DICER and RNA represents a captivating molecular choreography with far-reaching biological and clinical significance.

Subject of Research: Structural dynamics and functional mechanisms of the RNA-processing enzyme DICER during substrate binding and cleavage.

Article Title: DICER cleavage fidelity is governed by 5′-end binding pockets.

Article References: Ngo, M.K., Le, C.T. & Nguyen, T.A. DICER cleavage fidelity is governed by 5′-end binding pockets. Nature (2026). https://doi.org/10.1038/s41586-026-10211-5

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41586-026-10211-5