Mt. Tosteson et al., RECONSTITUTION OF THE INFLUENZA-VIRUS M(2) ION-CHANNEL IN LIPID BILAYERS, The Journal of membrane biology, 142(1), 1994, pp. 117-126
M(2), an integral membrane protein of influenza A virus, was purified
from either influenza A virus infected CV-1 cells or from Spodoptera f
rugiperda (Sf9) cells infected with a recombinant-M(2) baculovirus. Th
e purified protein, when incorporated into phospholipid bilayer membra
nes, produced ion-permeable channels with the following characteristic
s: (1) The channels appeared in bursts during which unit conductances
of diverse magnitudes (25-500 pS) were observed. (2) The most probable
open state was usually the lowest unit conductance (25-90 pS). (3) Th
e channels were selective for cations; t(Na) = 0.75 when 150 mM NaCl b
athed both sides of the membrane. (4) Amantadine reduced the probabili
ty of opening of the high conductance state and also the conductance o
f the most probable state. (5) Reducing pH increased the mean current
through the open channel as well as the conductance of the most probab
le state. (6) The sequence of selectivity for group IA monovalent cati
ons was Rb > K > Cs similar to Na > Li. The pH activation, amantadine
block and ion selectivity of the M(2) protein ion channel in bilayers
are consistent with those observed on expression of the M(2) protein i
n oocytes of Xenopus laevis as well as for those predicted for the pro
posed role of an ion channel in the uncoating process of influenza vir
us. The finding that the M(2) protein has intrinsic ion channel activi
ty supports the hypothesis that it has ion channel activity in the inf
luenza virus particle.