Hierarchical Assembly Pathways of Spermine-Induced Tubulin Conical-Spiral Architectures

Tubulin, an essential cytoskeletal protein, assembles into various morphologies by interacting with array of cellular factors. One these factors is the endogenous polyamine spermine, which may promote and stabilize tubulin assemblies. Nevertheless, assembled structures their formation pathways are poorly known. Here we show that spermine induced in vitro assembly several hierarchical architectures based on a conical-spiral subunit. Using solution X-ray scattering cryo-TEM, found progressive increase concentration dimers conical-frustum-spirals increasing length, containing up to three helical turns. The subunits turns were then tubules through base-to-top packing formed antiparallel bundles distorted hexagonal symmetry. Further led inverted bundles. Time-resolved experiments revealed assemblies at higher concentrations from intermediates, similar those low concentrations. These results distinct classical transition between twisted ribbons, helical, tubular assemblies, provide insight versatile can form. Furthermore, they contribute our understanding interactions control composition construction protein-based biomaterials.