Transverse tubules (T-tubules) are invaginations of the muscle plasma membrane that facilitate rapid transmission of action potentials, ensuring synchronized muscle contraction. Despite their essential role in muscle physiology, the mechanisms underlying T-tubule formation remain elusive. Here, we identify LUBEL/RNF31, a ubiquitin E3 ligase responsible for linear (M1-linked) ubiquitination, as a key regulator of T-tubule biogenesis in Drosophila. Loss of LUBEL leads to Amphiphysin (Amph)-positive membrane sheets instead of tubular networks. The ubiquitin ligase activity of LUBEL and direct interaction with Amph, a BAR domain protein involved in membrane tubulation, are crucial for proper T-tubule morphology. LUBEL and M1-linked ubiquitin chains assemble into puncta on membranes through multivalent interactions, facilitating Amph-mediated tubulation. Notably, the Amph-LUBEL/RNF31 interaction is evolutionarily conserved across species, underscoring a fundamental role for linear ubiquitination in membrane remodeling. Our findings uncover an unexpected function of linear ubiquitination in membrane deformation driven by BAR proteins.

The authors declare that they have no competing interests.