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EnsembleDesign: messenger RNA design minimizing ensemble free energy via probabilistic lattice parsing
Ning Dai1, Tianshuo Zhou1, Wei Yu Tang1
1School of Electrical Engineering and Computer Science, Oregon State University, Corvallis, OR 97330, United States.
Motivation:
The task of designing optimized messenger RNA (mRNA) sequences has received much attention in recent years, thanks to breakthroughs in mRNA vaccines during the COVID-19 pandemic. Because most previous work aimed to minimize the minimum free energy (MFE) of the mRNA in order to improve stability and protein expression, which only considers one particular structure per mRNA sequence, millions of alternative conformations in equilibrium are neglected. More importantly, we prefer an mRNA to populate multiple stable structures and be flexible among them during translation when the ribosome unwinds it.
Results:
Therefore, we consider a new objective to minimize the ensemble free energy of an mRNA, which includes all possible structures in its Boltzmann ensemble. However, this new problem is much harder to solve than the original MFE optimization. To address the increased complexity of this problem, we introduce EnsembleDesign, a novel algorithm that employs continuous relaxation to optimize the expected ensemble free energy over a distribution of candidate sequences. EnsembleDesign extends both the lattice representation of the design space and the dynamic programming algorithm from LinearDesign to their probabilistic counterparts. Our algorithm consistently outperforms LinearDesign in terms of ensemble free energy, especially on long sequences. Interestingly, as byproducts, our designs also enjoy lower average unpaired probabilities (which correlates with degradation) and flatter Boltzmann ensembles (more flexibility between conformations).
Availability And Implementation:
Our code is available on: https://github.com/LinearFold/EnsembleDesign.
Insights
Optimizing messenger RNA (mRNA) sequences requires considering all possible structures, not just one. Our new algorithm, EnsembleDesign, minimizes ensemble free energy for more flexible and stable mRNA designs.
Area of Science:
- Computational Biology
- Bioinformatics
- Molecular Biology
Background:
- Messenger RNA (mRNA) sequence design is crucial for applications like vaccines.
- Previous methods focused on minimizing minimum free energy (MFE), neglecting alternative mRNA conformations.
- Optimal mRNA function requires flexibility among multiple stable structures during translation.
Purpose of the Study:
- To develop a novel algorithm for optimizing mRNA sequences by minimizing ensemble free energy.
- To address the computational complexity of optimizing the entire Boltzmann ensemble of mRNA structures.
Main Methods:
- Introduced EnsembleDesign, a novel algorithm using continuous relaxation.
- Extended existing lattice representation and dynamic programming to probabilistic approaches.
- Optimized expected ensemble free energy over a distribution of candidate sequences.
Main Results:
- EnsembleDesign outperforms LinearDesign in minimizing ensemble free energy, particularly for longer sequences.
- Ensemble designs exhibit lower average unpaired probabilities, reducing degradation.
- Generated mRNA sequences demonstrate increased flexibility with flatter Boltzmann ensembles.
Conclusions:
- Minimizing ensemble free energy is a more effective objective for mRNA sequence design.
- EnsembleDesign provides a robust method for generating optimized mRNA sequences with improved stability and flexibility.
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