Multiscale Simulations of HIV capsid assembly and RNA

Informazioni relative al progetto

SimViRNA

ID dell’accordo di sovvenzione: 101109916

DOI

10.3030/101109916

Progetto chiuso

Data della firma CE 19 Aprile 2023

Data di avvio 1 Luglio 2023

Data di completamento 30 Giugno 2026

Finanziato da

• Marie Skłodowska-Curie Actions (MSCA)

Costo totale

Nessun dato

Contributo UE

€ 265 099,20

Coordinato da

SCUOLA INTERNAZIONALE SUPERIORE DI STUDI AVANZATI DI TRIESTE
Italy

Periodic Reporting for period 2 - SimViRNA (Multiscale Simulations of HIV capsid assembly and RNA)

Periodo di rendicontazione: 2025-07-01 al 2026-06-30

Sintesi del contesto e degli obiettivi generali del progetto

This project aims to establish new approaches toward large-scale simulations of biomolecular systems. We concretely seek to develop bottom-up coarse-grained models for the immature HIV CA-SP1 lattice including protease dimers as well as for RNA systems. Proteolytic cleavage of the CA-SP1 junction is an essential process for disassembly of the immature HIV lattice and hence critical to HIV infectivity. How the protease processes the immature HIV lattice and hence triggers its disassembly has remained an open question of high therapeutical interest that we address in this project. To this purpose, we have performed structural modelling of the CA-SP1/protease complex and performed extensive atomistic simulations that we subsequently used to build large-scale coarse-grained models. Development of such models that exhibit realistic affinities between the binding partners is a major difficulty that we solved by designing a new machine-learning technique. In this way, we are able to simulate the immature HIV lattice that is composed of more than 3100 proteins exposed to protease dimers. Furthermore, we have implemented a bond-cleavage mechanism for the CA-SP1 junction in the presence of protease dimers. Performing reactive, coarse-grained simulations for this system, we aim to toward a mechanistic understanding of how proteases cooperatively disassemble the immature HIV lattice. Such insight is highly relevant for the design of new drugs inhibit HIV maturation through stabilization of the immature HIV lattice such as bevirimat.
Another objective this project aims to work toward is an accurate atomistic/coarse-grained (MM/CG) model for RNA. Atomistic simulations of RNA macromolecules such as the ribosome are computationally too expensive. Long-range or cooperative effects, however, often play an important role in the conformational behavior of local domains. A pure coarse-grained representation, on the other hand, is of too low resolution to address fine-grained structural changes. Thus, we seek to resolve this dilemma by paving the way for a hybrid model in which critical parts of the system are atomistically resolved, whereas the surrounding is described by a coarse-grained model. In this way, we aim to lay the methodological foundation for a new simulation standard, that facilitates the simulation of drug binding to RNA target-sites while capturing the macromolecular environment.

Lavoro eseguito dall’inizio del progetto fino alla fine del periodo coperto dalla relazione e principali risultati finora ottenuti

Within this project, an experimental pdb-structure for a protease-peptide complex was used to build a structural model for a protease-dimer bound to a CA-SP1 site within the hexameric, immature HIV Gag-lattice. This represents one of the very first structural models for how proteases access the Gag-lattice for subsequent cleavage. Performing atomistic simulations starting from this complex structure, we have monitored that protease-binding induces structural changes in the lattice but not significant remodeling. To better understand large-scale remodeling as it occurs during HIV maturation, we have developed a coarse-grained model for this system. One of the main challenges here is to accurately describe affinities between different CA-SP1 monomers as well as between protease and CA-SP1, especially since binding/unbinding-events are difficult to sample for such large systems. We have resolved this issue by developing a new machine-learning method that represents a regularized version of relative entropy minimization. This new approach includes a quadratic bias on an empirical binding-affinity in its loss-function. In this way, it allows for accurate description of the complex structure as well as for the binding affinity. The method has been designed to guarantee maximum practicality, which means that no additional terms in the coarse-grained force fields or implementations in the simulation engine are required. Furthermore, we have demonstrated that hexameric CA-SP1 unit-models are transferable to simulate an entire immature HIV lattice. To simulate large-scale immature lattice remodeling triggered by proteolytic cleavages, we have developed a simulation routine in openmm that includes a CA-SP1 cleavage mechanism in the presence of protease. Large-scale simulations have been performed with this new model, yielding fundamental new insight into how proteolytic cleavages drive remodeling of the immature CA-SP1 lattice. In conclusion, these simulations support a model of delayed outlier formation (including dissociation of cleaved particles) after proteolytic cleavage expanding from lattice edges and gaps. Thus, the simulations align with the hypothesis of a combination of displacive remodeling and partial disassembly rather than a uniform conversion mechanism for HIV maturation.
Development of a new coarse-grained model for RNA has revealed a dominant impact of sugar puckering on the thermodynamic behavior of RNA. Moreover, simulations performed by us show critical misdescription of sugar puckering also in atomistic force fields. For this reason, we have devised a new machine learning workflow to optimize sugar puckering in RNA based on experimental (NMR) data. Optimized atomistic and coarse-grained models will allow for future merging in a hybrid model.

Progressi oltre lo stato dell’arte e potenziale impatto previsto (incluso l’impatto socioeconomico e le implicazioni sociali più ampie del progetto fino ad ora)

Most researchers perform coarse-grained simulations using existing top-down models, such as MARTINI. Developing a new coarse-grained model for the immature CA-SP1 lattice of HIV in a bottom-up approach, i.e. in consistency with atomistic data, is therefore clearly beyond state-of-the-art. In addition, molecular simulations usually also do not include reactions, such as proteolytic bond-cleavage. Implementation of such a mechanism into a simulation model is therefore also a very important extension over standard protocols. This approach is straightforwardly transferable also to other molecular systems, meaning that the newly developed approach and simulation protocol can serve as a template also for other researchers. Thus, it facilitates numerous future extensions that can have a high pharmaceutical impact. For instance, it allows one to also investigate how drugs can stabilize the immature lattice to undermine HIV maturation and hence devise new drug-targeting strategies.