Structure of the Argonaute Maturation Complex Guides Rational RNA Therapeutic Design
核心洞察
Researchers at IBS and Seoul National University have revealed the first near-atomic resolution structure of the Argonaute (搜索) maturation complex, showing how chaperone proteins hold Argonaute in an open conformation for miRNA loading.
The study demonstrates that miRNA is not passive cargo but an active molecular cofactor that directly guides Argonaute (搜索) protein folding, a finding that reshapes understanding of RISC assembly.
An experimental system was established that reproduces Argonaute (搜索) loading outside cells, enabling direct evaluation of how chemical modifications in therapeutic siRNAs affect assembly and function.
A research team led by Director Kim V. Narry at the Center for RNA Research within the Institute for Basic Science (搜索) (IBS), together with Professor Roh Soung-Hun at Seoul National University, has revealed for the first time how Argonaute (搜索)—the core protein responsible for gene silencing—acquires its functional form by loading small RNAs. The findings, published in Nature on June 10, establish a new molecular framework for the rational design of RNA therapeutics.
The work addresses a fundamental knowledge gap that has persisted despite the approval of eight small interfering RNA (siRNA) drugs worldwide for genetic diseases. Scientists had not fully understood how bulky miRNA are loaded into Argonaute (搜索) and assembled into an active gene-silencing complex, limiting efforts to design more effective RNA therapeutics.
Capturing the Argonaute (搜索) Maturation Complex
To address this question, the researchers successfully isolated and purified a previously unknown Argonaute (搜索) maturation complex (AMC), in which Argonaute is associated with the chaperone proteins Hsp90 (搜索). Using state-of-the-art cryo-electron microscopy (cryo-EM), they determined the three-dimensional structure of the complex at near-atomic resolution.
The structure revealed that chaperone proteins hold Argonaute (搜索) in an unusually open conformation, creating enough space for a miRNA to enter. Once the miRNA is loaded, the chaperones are released and Argonaute folds into its mature functional form capable of silencing genes. When the team reconstituted the Argonaute assembly process in vitro, the assembled Argonaute complex accurately cleaved its target genes.
RNA as an Active Molecular Cofactor
Unexpectedly, the study showed that the RNA itself plays a far more active role than previously recognized. The researchers found that miRNA is not merely cargo delivered to Argonaute (搜索). Instead, the miRNA acts as a molecular cofactor that helps guide Argonaute folding. In the absence of a proper miRNA, Argonaute failed to acquire its functional structure.
"Researchers have traditionally focused on protein structures after they have already formed. In this study, we were able to directly observe the process by which a protein acquires its function," said Professor Roh Soung-Hun, co-corresponding author of the study. "The findings provide a new perspective on how chaperones and RNA cooperate to create functional biological molecules."
Structural Requirements for Efficient Assembly
The team further identified key structural features required for efficient Argonaute (搜索) assembly. They showed that miRNA must possess specific chemical characteristics, retain a two-stranded structure, and have an optimal length of approximately 20–24 nucleotides. These properties closely match those found in naturally occurring miRNAs and therapeutic siRNAs.
Importantly, the researchers established an experimental system that faithfully reproduces Argonaute (搜索) loading and RISC assembly outside living cells. Using this platform, they directly examined how chemical modifications commonly used in therapeutic siRNAs affect Argonaute assembly and function.
Implications for RNA Therapeutic Design
"This achievement provides, for the first time, a molecular basis for RNA therapeutic design, which has until now relied largely on trial and error," said Director Kim V. Narry, co-corresponding author of the study. "We expect these findings will contribute to the development of safer and more effective RNA therapeutics."
Beyond advancing understanding of RNA biology, the study provides broader insight into how molecular chaperones cooperate with biological ligands to guide protein folding. The Ministry of Science and ICT (MSIT) of South Korea highlighted that the findings enhance both the efficiency and the translational potential of RNA therapeutic design, particularly for treating intractable diseases caused by gene overexpression.