European Biophysics Journal

, Volume 34, Issue 1, pp 52–66

The influenza virus ion channel and maturation cofactor M2 is a cholesterol-binding protein

  • Cornelia Schroeder
  • Harald Heider
  • Elisabeth Möncke-Buchner
  • Tse-I Lin
Article

DOI: 10.1007/s00249-004-0424-1

Cite this article as:
Schroeder, C., Heider, H., Möncke-Buchner, E. et al. Eur Biophys J (2005) 34: 52. doi:10.1007/s00249-004-0424-1

Abstract

The influenza-virus M2 protein has proton channel activity required for virus uncoating and maturation of hemagglutinin (HA) through low-pH compartments. The proton channel is cytotoxic in heterologous expression systems and can be blocked with rimantadine. In an independent, rimantadine-resistant function, M2, interacting with the M1 protein, controls the shape of virus particles. These bud from cholesterol-rich membrane rafts where viral glycoproteins and matrix (M1)/RNP complexes assemble. We demonstrate that M2 preparations from influenza virus-infected cells and from a baculovirus expression system contain 0.5–0.9 molecules of cholesterol per monomer. Sequence analyses of the membrane-proximal M2 endodomain reveal interfacial hydrophobicity, a cholesterol-binding motif first identified in peripheral benzodiazepine receptor and human immunodeficiency virus gp41, and an overlapping phosphatidylinositol 4,5-bisphosphate-binding motif. M2 induced rimantadine-reversible cytotoxicity in intrinsically cholesterol-free E. coli, and purified E. coli-expressed M2 functionally reconstituted into cholesterol-free liposomes supported rimantadine-sensitive proton translocation. Therefore, cholesterol was nonessential for M2 ion-channel function and cytotoxicity and for the effect of rimantadine. Only about 5–8% of both M2 preparations, regardless of cholesterol content, associated with detergent-resistant membranes. Cholesterol affinity and palmitoylation, in combination with a short transmembrane segment suggest M2 is a peripheral raft protein. Preference for the raft/non-raft interface may determine colocalization with HA during apical transport, the low level of M2 incorporated into the viral envelope and its undisclosed role in virus budding for which a model is presented. M2 may promote clustering and merger of rafts and the pinching-off (fission) of virus particles.

Keywords

M2 ion-channel proteinPeripheral raft proteinVirus buddingMembrane fissionInfluenza virus

Abbreviations

CRAC

Cholesterol recognition/interaction amino acid consensus

DMPC

l-α-dimyristoylphosphatidylcholine

DRM

Detergent-resistant membrane

HA

Hemagglutinin

HDL

High-density lipoprotein

KPS

Potassium phosphate buffer with K2SO4

LDL

Low-density lipoprotein

MDCK

Madin-Darby canine kidney

NA

Neuraminidase

NaPS

Sodium phosphate buffer with Na2SO4

Ni-NTA

Nickel-nitrilotriacetic acid

OG

N-octyl-β-d-glucopyranoside

PM

Plasma membrane

PS

Phosphatidylserine

RNP

Ribonucleoprotein

Sf9

Spodoptera frugiperda

TDC

Taurodeoxycholate

TGN

trans-Golgi network

TM

Transmembrane

T. ni

Trichoplusia ni

TX-100

Triton X-100

Φ

Hydrophobic amino acid

Copyright information

© EBSA 2004

Authors and Affiliations

  • Cornelia Schroeder
    • 1
    • 2
  • Harald Heider
    • 3
  • Elisabeth Möncke-Buchner
    • 3
  • Tse-I Lin
    • 3
    • 4
  1. 1.Abteilung Virologie, Institut für Mikrobiologie und HygieneUniversität des Saarlandes, Homburg/SaarHomburgGermany
  2. 2.Jadolabs GmbHDresdenGermany
  3. 3.Institut für Virologie, Universitätsklinikum CharitéHumboldt-Universität zu BerlinBerlinGermany
  4. 4.Tibotec BVDVMechelenBelgium