Intrinsic Disorder and Salt-dependent Conformational Changes of the N-terminal Region of TFIP11 Splicing Factor

Tuftelin Interacting Protein 11 (TFIP11) was recently identified as a critical human spliceosome assembly regulator, interacting with multiple spliceosome proteins and localises in several membrane-less organelles. However, there is a lack of structural information on TFIP11, limiting the rationalisation of its biological role. TFIP11 has been predicted as a highly disordered protein, and more specifically concerning its N-terminal (N-TER) region. Intrinsically disordered proteins (IDPs) lack a defined tertiary structure, existing as a dynamic conformational ensemble, favouring their role as hubs in protein-protein and protein-RNA interaction networks. Furthermore, IDPs are involved in liquid-liquid phase separation (LLPS), driving the formation of subnuclear compartments. Combining disorder prediction, molecular dynamics, and spectroscopy methods, this contribution shows the first evidence TFIP11 N-TER may be described as a polyampholytic IDP, exhibiting a structural duality with the coexistence of ordered and disordered assemblies, depending on the ionic strength of the protein environment. Increasing the salt concentration enhances the protein conformational flexibility, presenting a fuzzier conformational landscape, a more globule-like shape, and an unstructured arrangement that could favour LLPS segregation and protein-RNA interaction. The regions mostly composed of charged and hydrophilic residues are the most impacted, including the G-Patch domain which is of crucial importance to TFIP11 function.