Membrane remodeling by the M2 amphipathic helix drives influenza virus membrane scission

Agnieszka Martyna,Saipraveen Srinivasan,Matthew D Badham,Basma Bahsoun,Jeremy S Rossman,Mark J Howard

doi:10.1038/srep44695

Abstract

Membrane scission is a crucial step in all budding processes, from endocytosis to viral budding. Many proteins have been associated with scission, though the underlying molecular details of how scission is accomplished often remain unknown. Here, we investigate the process of M2-mediated membrane scission during the budding of influenza viruses. Residues 50–61 of the viral M2 protein bind membrane and form an amphipathic α-helix (AH). Membrane binding requires hydrophobic interactions with the lipid tails but not charged interactions with the lipid headgroups. Upon binding, the M2AH induces membrane curvature and lipid ordering, constricting and destabilizing the membrane neck, causing scission. We further show that AHs in the cellular proteins Arf1 and Epsin1 behave in a similar manner. Together, they represent a class of membrane-induced AH domains that alter membrane curvature and fluidity, mediating the scission of constricted membrane necks in multiple biological pathways.

Highlights

Membrane scission is a crucial step in all budding processes, from endocytosis to viral budding
Protein modeling and nuclear magnetic resonance (NMR) experiments have suggested that the first 16 amino acids of the A/Udorn/72 influenza virus M2 protein cytoplasmic tails (CT) form an amphipathic helix; the structure of the full AH domain and its dependency on lipid binding for α-helix formation is not known[16,17,20]
synchrotron radiation circular dichroism (SRCD) spectra were obtained for M2AH in detergent-free solution and in the presence of large unilamellar vesicles (LUVs)

Summary

Introduction

Membrane scission is a crucial step in all budding processes, from endocytosis to viral budding. We further show that AHs in the cellular proteins Arf[1] and Epsin[1] behave in a similar manner Together, they represent a class of membrane-induced AH domains that alter membrane curvature and fluidity, mediating the scission of constricted membrane necks in multiple biological pathways. Membrane insertion of cationic AH domains, such as those found in Epsin[1] and in antimicrobial peptides, can induce membrane curvature and may play a more direct role in membrane remodeling and scission[7,8] Because of their ability to sense and/or induce membrane curvature, AHs have been implicated in a wide range of membrane scission events, Arf[1] for COP-vesicle budding[9], Endophilin for non-clathrin-mediated endocytosis[10,11], CHMP4b for multi-vesicular body (MVB) budding[12] and M2 for influenza virus budding[13]. It is at this membrane neck www.nature.com/scientificreports/

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