Polymerization of Tetraspanin 7 into Helical Transmembrane Skeletons for Tubular Membrane Stabilization

Tubular cell membrane protrusions, such as filopodia1, dendrites2, tunneling nanotubes (TNTs)3 and retraction fibers4, are prevalent on the cell surface. They play crucial roles in various physiological processes and disease states, including angiogenesis, wound healing, and cancer metastasis5-7. The shaping and stabilization of these protrusions are crucial for their function, and the molecular machineries involved have long been an active area of investigation. Here we employed an integrative approach combining live-cell imaging, in vitro reconstitution, and in situ cryo-EM analysis to reveal that the transmembrane protein tetraspanin 7 (TSPAN7) senses membrane curvature and polymerizes into a helical configuration on highly curved tubular membranes. These spirals act as a "transmembrane skeleton", effectively maintaining the structural integrity of membrane protrusions under mechanical stress. Our findings reveal a previously unreported assembly strategy for transmembrane proteins and a mechanism for maintaining tubular membrane protrusions.