Abis, G. | bioRxiv Science

bioRxiv2025

Structural mechanisms of drebrin-mediated F-actin network modulation

Drebrin modulates F-actin networks and links them to other intracellular components, regulating crucial processes including neuritogenesis, synaptic plasticity, virus internalisation and cancer invasion. Using single-particle cryo-EM we characterise drebrins interaction with F-actin through two separate conserved actin binding domains (ABD1 and ABD2), revealing structural bases for its F-actin-modulating properties. We describe a multimodal interaction where drebrins ABD1 can adopt two conformations and a long flexible loop connecting to ABD2 allows the two ABDs to occupy multiple relative positions along F-actin. Despite harbouring two separated ABDs, we find that drebrin is not a strong direct F-actin bundler. Drebrins ABDs bind across multiple actin protomers and their subdomains and modify the longitudinal inter-protomer interface, explaining their F-actin stabilising properties. Furthermore, we show drebrins binding site on F-actin is shared with other critical actin-binding and regulatory proteins, explaining their competitive displacement.

biochemistry↗

bioRxiv2024

An intrinsically disordered RNA-binding region provides local target selectivity and is essential for LARP6 function.

Intrinsically disordered regions (IDRs) are prevalent in RNA-binding proteins (RBPs), yet their roles in RNA interactions remain poorly defined. Here, we examined the structured and disordered RNA-binding activities of LARP6, an RBP with a diverse RNA-binding repertoire. Using mass spectrometry-based RNA interaction mapping in living cells, we identified direct LARP6-RNA contacts within both the structured La-module and its flanking IDRs. Mutagenesis combined with individual-nucleotide resolution UV crosslinking and immunoprecipitation (iCLIP) revealed the La-module, but not the IDRs, as essential for LARP6 binding to RNA. Deletion of the N-terminal IDR broadened the footprints of LARP6 on RNA, uncovering a role in RNA-binding selectivity. Mechanistically, this is achieved through restricting the conformational flexibility of the adjacent La-module. The IDR-mediated RNA-binding selectivity is critical for LARP6-driven cancer cell viability and invasion. Our findings uncover a previously unrecognised critical function for IDRs in promoting selective RBP-RNA interactions, which operates through conformational restriction.

biochemistry↗