Characterization of the ion channels formed by poliovirus in planar lipid membranes

Abstract

The steps in poliovirus infection leading to viral entry and uncoating are not well understood. Current evidence suggests that the virus first binds to a plasma membrane-bound receptor present in viable cells, leading to a conformational rearrangement of the viral proteins such that the virus crosses the membrane and releases the genomic RNA. The studies described in this report were undertaken to determine if poliovirus (160S) as well as one of the subviral particles (135S) could interact with membranes lacking poliovirus receptors in an effort to begin to understand the process of uncoating of the virus. We report that both forms of viral particles, 160S and 135S, interact with lipid membranes and induce the formation of ion-permeable channels in a manner that does not require acid pH. The channels induced by the viral particles 160S have a voltage-dependent conductance which depends on the ionic composition of the medium. Our findings raise the possibility that viral entry into cells may be mediated by direct interaction of viral surface proteins with membrane lipids.Poliovirus is a prototypical member of the Picornaviridae family. The plus-stranded RNA genome of this nonenveloped virus is tightly packed within an icosahedrally symmetric spherical shell which is composed of 60 copies of each of four proteins (VP1 to VP4). The myristoylated VP4 and the aminoterminal sequences of the other three capsid proteins are located on the inner surface of the poliovirus virion (8).Infection of cells by poliovirus starts as the virus particle attaches to the receptor at the cell membrane (2, 6). Receptor binding leads to a conformational transition that results in altered particles which lack VP4 and sediment with a coefficient of 135S (compared to 16 0S for the intact virion) (3a, 6, 9). This alteration in sedimentation behavior is further accompanied by the relocation and exposure of most of the aminoterminal regions of VP1 from the inner to the outer surface of the virion shell. Exposure of the amino-terminal regions of VP1 confers membrane binding properties to the 135S particles, which has been observed by Fricks and Hogle (5), using a liposome flotation method. However, the subsequent stages of penetration and uncoating remain poorly defined.For viral replication to take place, the viral RNA must traverse the plasma membrane and be uncoated and released to the cytosol. Several hypotheses have been put forth to explain viral entry and uncoating, ranging from receptor-mediated endocytosis of the whole virion, to direct penetration of the plasma membrane by the 160S particle (hereafter referred to as simply 160S), to entry of the subviral particle 135S by either of those mechanisms (references 1 and 13 and references therein). Binding and anchoring of the viral particle to a membrane are required steps in any of these hypotheses.In this report, we present evidence that domains of the native virion (160S) and the receptor-altered viral particle (135S) bind and interact with lipid bilayers to form ion-permeable channels...

Interaction of Poliovirus with Its Receptor Affords a High Level of Infectivity to the Virion in Poliovirus Infections Mediated by the Fc Receptor

“…Infectivity of the 135S particle was not detected in this study, suggesting that an essential interaction between PV1 and the cell surface probably occurs during the process of conformational change to the 135S particle. This notion is supported by the following; infectosome formation was proposed for the uncoating of human rhinovirus (28), ion channel formation by PV1 may be a result of a direct interaction of the capsid protein with the plasma membrane lipid bilayer (48), and the cold-adapted phenotype of PV1 mutants suggests that virion conformational alteration to the 135S particle is not an essential event for the uncoating process (7). It should be noted that the assay used for Fig.…”

Variation in Liposome Binding among Enteroviruses

“…The two types of channels may have different functions in the infection process, or one (or both) of them may be an artifact of the experimental system. Based on the con-ductance measurements, it was estimated that the channel formed by the 135S particle should have a diameter of approximately 2 nm, which could in theory allow the RNA to pass through (Tosteson and Chow, 1997). Our finding that the 135S particle of PV3 did not bind to liposomes while the native virion did might reflect the difference in the channels and the distinct functions that they possibly have in the course of infection.…”

“…Specifically, when the 135S particles are studied, they have already lost the majority of the VP4 protein that is needed in the cell entry (Moscufo et al, 1993) and may be important in the channel formation during the natural process. Furthermore, the native virions form smaller channels than the 135S particles do (Tosteson and Chow, 1997). Extrapolating from these observations, one could suggest that in the process of virus infection, the additional components available may participate in forming a larger channel.…”

“…When poliovirus particles bind to lipid bilayers, ionpermeable channels are formed (Tosteson and Chow, 1997). Both intact virions and 135S particles are capable of attaching to membranes, but the channels formed are different.…”

“…Both intact virions and 135S particles are capable of attaching to membranes, but the channels formed are different. Those formed by 135S are larger, and their permeability is independent of voltage or temperature (Tosteson and Chow, 1997). The two types of channels may have different functions in the infection process, or one (or both) of them may be an artifact of the experimental system.…”