Viral Membrane Channels: Role and Function in the Virus Life Cycle

Sze, Ching Wooen; Tan, Yee-Joo

The majority of the viroporins are important in the final stage of the viral life cycle because they facilitate the release of fully assembled virus particles from the host. In the non-enveloped virus, lysis of the host cells is commonly used to release infectious virions devoid of host membrane. In enteroviruses, the non-structural protein 2B forms pores in ER membrane, leading to leakage of calcium into the cytoplasm. Disruption of calcium homeostasis activates several host immune responses such as autophagy, which ultimately leads to cellular apoptosis (see review [41] ). For example, in Coxsackievirus, 2B has been found to localize to the ER and plasma membrane at different stages of the infection. A model has been proposed whereby 2B alters the permeability of the ER and plasma membrane to facilitate viral release by affecting the calcium content [39] . Subsequent viral release is most likely achieved through apoptosis induction via the calcium dependent mitochondrial pathway [40, 41] . In Poliomaviruses such as SV40, proliferation occurs in the nuclei and release of infectious particles occurs following cells' rupture [88] . VP4 of SV40 induces membrane perforation by forming toroidal pores, fusing the outer and inner leaflets of the lipid bilayers to initiate viral release. Mutational analysis indicated that Pro70 located within the hydrophobic region is essential for the membrane disruption ability of VP4 [47] .