TDP-43 multidomains and RNA modulate interactions and viscoelasticity in biomolecular condensates.

RNA-binding proteins form biomolecular condensates with RNA through phase separation, playing crucial roles in various cellular processes. Although intrinsically disordered regions (IDRs) are key drivers of phase separation, additional factors such as folded domains and RNA also influence condensate formation and physical properties. However, the molecular mechanisms underlying this regulation remain elusive. Here, using molecular dynamics simulations, we investigate how the multidomain structure of TDP-43, which consists of its IDR, RNA recognition motifs (RRMs), and N-terminal domain (NTD), interacts with RNA and affects the characteristics of phase separation. Our analysis reveals that interactions via the IDR are dominant in all domain constructs, particularly around residues R268-F276. RRM2 increases condensate packing, whereas NTD decreases it. Upon RNA binding, several intermolecular interactions of TDP-43 are replaced by TDP-43-polyA interactions, altering viscoelastic properties of the condensate. Specifically, RRMs enhance viscosity, whereas the NTD reduces it. The presence of polyA increases elasticity, making viscosity and elasticity comparable in magnitude. These findings suggest that the multidomain structure of TDP-43 and its RNA interactions orchestrate condensate organization, modulating their viscoelastic properties.