Structural inhibition of dynamin-mediated membrane fission by endophilin.

Annika Hohendahl,Peter S Shen,Frédéric Humbert,Valentina Galli,Adam Frost,Pietro De Camilli,Aurélien Roux,Nathaniel Talledge

doi:10.7554/elife.26856

Abstract

Dynamin, which mediates membrane fission during endocytosis, binds endophilin and other members of the Bin-Amphiphysin-Rvs (BAR) protein family. How endophilin influences endocytic membrane fission is still unclear. Here, we show that dynamin-mediated membrane fission is potently inhibited in vitro when an excess of endophilin co-assembles with dynamin around membrane tubules. We further show by electron microscopy that endophilin intercalates between turns of the dynamin helix and impairs fission by preventing trans interactions between dynamin rungs that are thought to play critical roles in membrane constriction. In living cells, overexpression of endophilin delayed both fission and transferrin uptake. Together, our observations suggest that while endophilin helps shape endocytic tubules and recruit dynamin to endocytic sites, it can also block membrane fission when present in excess by inhibiting inter-dynamin interactions. The sequence of recruitment and the relative stoichiometry of the two proteins may be critical to regulated endocytic fission.

Highlights

Dynamin is a 97 kDa GTPase that mediates membrane fission in several endocytic routes
The contrast of the endophilin-dynamin tubules was stronger, and these tubules appeared thicker under Differential Interference Contrast (DIC) microscopy, probably reflecting the co-assembly of endophilin and dynamin
Our results show that the non-physiological 4x molar excess of endophilin inhibits fission completely by blocking dynamin constriction

Summary

Introduction

Dynamin is a 97 kDa GTPase that mediates membrane fission in several endocytic routes. Polymeric forms have a GTPase activity increased up to a 1000-fold over basal hydrolysis rates (Stowell et al, 1999). This increase is proposed to result from trans interactions between GTPase (G) domains of adjacent turns of a dynamin helical polymer (Chappie et al, 2010). Constriction of the dynamin polymer is required for membrane fission (Antonny et al, 2016), but how GTPase activity drives constriction is still debated. The disassembly model proposes that dynamin assembles into a highly constricted helix in the GTP-loaded state and that GTP-hydrolysis-dependent disassembly is required for fission (Shnyrova et al, 2013).

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Conclusion