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Gaurav, K.

Publications and source records attributed to Gaurav, K..

8 recordsLinked to original sources

Active Learning-Guided Peptide Design for Modulating Condensate Properties upon Recruitment

The physical properties of biomolecular condensates, which form through phase separation, are central to their organisation and function and are increasingly implicated in disease mechanisms. To function correctly, condensates often recruit client biomolecules such as peptides and RNAs. This recruitment is not only essential to condensate biology but also offers an opportunity to engineer clients that tune the material properties of the condensate. Here we studied the previously characterised MUT-16 condensate, the scaffold of a membraneless organelle in C. elegans that recruits the N-terminal prion-like domain of MUT-8, a process essential for RNA silencing. We used coarse-grained molecular dynamics simulations to model and design peptide variants that interact with the scaffold protein MUT-16 and modulate its physical properties. To guide this design efficiently, we applied an active learning framework, which combines Bayesian optimization with neural networks to iteratively select the most informative peptide variants for simulation. This strategy reduced the number of simulations required while allowing the model to learn the sequence-property relationships that govern condensate behavior. Overall, this physics-based, learning-guided framework offered a computational approach to exploring how peptides can be engineered to influence condensate properties, and may inform the rational design of synthetic condensates.

bioengineering↗

Atomistic simulations reveal sub-μs contact dynamics in MUT-16 condensates.

Phase separation of proteins gives rise to biomolecular condensates, which function as membraneless organelles that spatially and temporally organize cellular functions. Such condensates are often formed by intrinsically disordered regions of proteins (IDRs), whose multivalent and transient interactions govern condensate structure and dynamics. However, elucidating the molecular determinants of these interactions at atomistic resolution remains challenging. Here, we present a total of 10 {micro}s of atomistic molecular dynamics simulations of a phase-separated condensate formed by the foci-forming region (FFR) of MUT-16. MUT-16 serves as a scaffold of the Mutator foci germ granules in Caenorhabditis elegans and is essential for transposon silencing. MUT-16 FFR is enriched in polar uncharged (Gln, Asn), charged, aromatic, and Pro residues, raising the question of how these amino acids interact within condensates. We find that most contacts are short lived, typically breaking within a few nanoseconds (ns), with a median life time of 9.8 ns. A smaller fraction persist for much longer timescales (> 100 ns). We characterized the relative contributions of different amino acids and specific interaction types, including hydrogen bonding, cation-{pi} interactions,{pi} -{pi} stacking, and salt bridges and theirs dynamics. We further examined the roles of water and ions in modulating condensate interactions, including ion-mediated bridging between similarly charged residues. Our results reveal that salt bridges, cation-{pi} interactions, Na+ ions, and water in the condensate are key determinants of contact dynamics in MUT-16 FFR condensates. In parallel, we show that these condensates exhibit upper-critical solution temperature (UCST) phase behavior in vitro, providing a coherent framework to explain both the loss of Mutator foci at elevated temperatures in vivo and the scaffolding role of MUT-16 at lower temperatures.

biochemistry↗

Proteolytic Control of an Auto-inhibitory Intrinsically Disordered Region Governs Small RNA Selectivity in Argonaute Proteins

Argonaute proteins are central to small RNA-mediated gene regulation, yet the mechanisms controlling their activity remain incompletely understood. We elucidate a novel regulatory mechanism governing small RNA loading into the C. elegans Argonaute proteins WAGO-1 and WAGO-3. We show that N-terminal intrinsically disordered regions (N-IDRs) of these proteins do not affect subcellular localization but play critical roles in small RNA loading. We demonstrate that the N-IDR-processing protease DPF-3 facilitates small RNA loading in a catalysis-independent manner. Catalysis by DPF-3 and a second protease APP-1 is required, however, for activity. Deletion of these N-IDRs results in loading of aberrant small RNA species that trigger erroneous gene silencing. Supported by atomistic molecular dynamics simulations, we propose a model in which N-IDRs can simultaneously act as tuneable gatekeepers that auto-inhibit small RNA loading and as regulators of Argonaute stability, representing a previously unrecognized layer of regulation in Argonaute activity in small RNA pathways.

molecular biology↗

Multiscale simulations of molecular recognition by phase separated MUT-16: A scaffolding protein of Mutator foci

Phase separation of proteins plays a critical role in cellular organisation. How phase separated protein condensates underpin biological function and how condensates achieve specificity remain elusive. We investigated the phase separation of MUT-16, a scaffold protein in Mutator foci, and its role in recruiting the client protein MUT-8, a key component in RNA silencing in C. elegans. We employed a multiscale approach that combined coarse-grained (residue-level CALVADOS2 and near-atomistic Martini3) and atomistic simulations. Simulations across different resolutions provide a consistent perspective on how MUT-16 condensates recruit MUT-8, enabling the fine-tuning of chemical details while balancing the computational cost. Both coarse-grained models (CALVADOS2 and Martini3) predicted the relative phase separation propensities of MUT-16s disordered regions, which we confirmed through in vitro experiments. Simulations also identified key sequence features and residues driving phase separation while revealing differences in residue interaction propensities between CALVADOS2 and Martini3. Furthermore, Martini3 and 350 {micro}s atomistic simulations on Folding@Home of MUT-8s N-terminal prion-like domain with MUT-16 M8BR cluster highlighted the importance of cation-{pi} interactions between Tyr residues of MUT-8 and Arg residues of MUT-16 M8BR. Lys residues were observed to be more prone to interact in Martini3. Atomistic simulations revealed that the guanidinium group of Arg also engages in sp2-{pi} interactions and hydrogen bonds with the backbone of Tyr, making Arg-Tyr interactions stronger than Lys-Tyr, where these additional favourable contacts are absent. In agreement with our simulations, in vitro co-expression pulldown experiments demonstrated a progressive loss of MUT-8 recruitment following the mutation of Arg in MUT-16 M8BR to Lys or Ala, confirming the critical role of Arg in this interaction. These findings advance our understanding of MUT-16 phase separation and subsequent MUT-8 recruitment, key processes in assembling Mutator foci that drive RNA silencing in C. elegans. Statement of SignificanceIn cells proteins phase separate and form condensates. These protein condensates can play important role in bringing molecules together and facilitate biochemical processes. In this work, we used molecular dynamics simulations to understand how MUT-16 phase separates and forms the scaffold of the so-called Mutator focus. Mutator foci produce small RNA which help to regulates genes. As the scaffold of the Mutator focus, MUT-16 recruit multiple proteins which are important for the production of such small RNAs.

bioinformatics↗

Harnessing Landrace Diversity Empowers Wheat Breeding for Climate Resilience

Breeding crops resilient to climate change is urgently needed to help ensure food security. A key challenge is to harness genetic diversity to optimise adaptation, yield, stress resilience and nutrition. We examined the genetic and phenotypic diversity of the A.E. Watkins landrace collection of bread wheat (Triticum aestivum), a major global cereal, through whole-genome re-sequencing (827 Watkins landraces and 208 modern cultivars) and in-depth field evaluation spanning a decade. We discovered that modern cultivars are derived from just two of the seven ancestral groups of wheat, leaving five groups as previously untapped sources for breeding. This provides access to landrace-specific functional variations using structured germplasm, genotyping and informatics resources. Employing complementary genetic populations and approaches, we identified thousands of high-resolution quantitative trait loci (QTL) and significant marker-trait associations for major traits, revealing many Watkins-unique loci that can confer superior traits in modern wheat. Furthermore, we identified and functionally verified causative genes for climate-change adaptation, nutritional enhancement and resistance to wheat blast. Finally, we assessed the phenotypic effects of 44,338 Watkins-unique haplotypes, introgressed from 143 prioritised QTL in the context of modern cultivars, bridging the gap between landrace diversity and current breeding. This study establishes a framework for systematically utilising genetic diversity in crop improvement to achieve sustainable food security.

plant biology↗

The wheat powdery mildew resistance gene Pm4 also confers resistance to wheat blast

Wheat blast, caused by the fungus Magnaporthe oryzae, threatens global cereal production since its emergence in Brazil in 1985 and recently spread to Bangladesh and Zambia. Here we demonstrate that the AVR-Rmg8 effector, common in wheat-infecting isolates, is recognised by the gene Pm4, previously shown to confer resistance to specific races of Blumeria graminis f.sp. tritici, the cause of powdery mildew of wheat. We show that Pm4 alleles differ in their recognition of different AVR-Rmg8 alleles, and some confer resistance only in seedling leaves but not spikes making it important to select for those alleles that function in both tissues. This study has identified a gene recognising an important virulence factor present in wheat blast isolates in Bangladesh and Zambia and represents an important first step towards developing durably resistant wheat cultivars for these regions.

plant biology↗

A wheat kinase and immune receptor form the host-specificity barrier against the blast fungus

Since emerging in Brazil in 1985, wheat blast has spread throughout South America and recently appeared in Bangladesh and Zambia. We show that two wheat resistance genes, Rwt3 and Rwt4, acting as host-specificity barriers against non-Triticum blast pathotypes encode a nucleotide-binding leucine-rich repeat immune receptor and a tandem kinase, respectively. Molecular isolation of these genes allowed us to develop assays that will ensure the inclusion of these two genes in the wheat cultivars to forestall the recurrence of blast host jumps.

plant biology↗

Evolution of the bread wheat D-subgenome and enriching it with diversity from Aegilops tauschii

Aegilops tauschii, the diploid wild progenitor of the D-subgenome of bread wheat, constitutes a reservoir of genetic diversity for improving bread wheat performance and environmental resilience. To better define and understand this diversity, we sequenced 242 Ae. tauschii accessions and compared them to the wheat D-subgenome. We characterized a rare, geographically-restricted lineage of Ae. tauschii and discovered that it contributed to the wheat D-subgenome, thereby elucidating the origin of bread wheat from at least two independent hybridizations. We then used k-mer-based association mapping to identify discrete genomic regions with candidate genes for disease and pest resistance and demonstrated their functional transfer into wheat by transgenesis and wide crossing, including the generation of a library of synthetic hexaploids incorporating diverse Ae. tauschii genomes. This pipeline permits rapid trait discovery in the diploid ancestor through to functional genetic validation in a hexaploid background amenable to breeding.

plant biology↗