Insights into the Structure of Intermediate Filaments.

Intermediate filaments (IFs) are central to the mechanical integrity of metazoan cells and play critical roles in various fundamental cellular and multicellular processes, including cell motility, signal transduction, and wound healing. To perform their functions, IF proteins self-assemble into nanoscale biopolymers, each exhibiting unique properties that are finely tuned to their specific roles across different tissue types. However, the 3D structure of IFs has remained largely unresolved due to their intrinsic flexibility and polymorphism. This chapter reviews recent advances in the structural analysis of IFs, with a focus on vimentin IFs (VIFs), which are featuring a helical tube with a central luminal fiber. We discuss how AlphaFold-based modeling, chemical cross-linking data, and cryo-electron microscopy (cryo-EM) reconstructions have been integrated to generate a detailed structural model of VIFs, highlighting key features such as the helical symmetry of the filaments and the nature of the luminal fiber. Additionally, we explore potential sources of IF polymorphism and their implications for the analysis of IF structures.