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

Sze, Ching Wooen; Tan, Yee-Joo

For the non-enveloped virus, Simian virus 40 (SV40) encodes up to three known pore forming proteins, VP2, VP3, and VP4, each of which is activated at a different stage of the life cycle with a different mechanism of action [44, [46] [47] [48] 87, 88] . Upon endocytosis into host via the caveolae-1 coated vesicles [89, 90] , the virus is translocated to the endoplasmic reticulum (ER) where reorganization of the capsid and subsequent escape of the viral particle into the cytosol occurs. VP2 and VP3 are proposed to be responsible for the escape of the virus into the cytosol as they are able to integrate into the ER membranes [44, 45, 47] . Virus-like particles devoid of VP2 and VP3 failed to traverse through the ER membrane into the cytoplasmic space [45] . Consistently, mutant viruses lacking VP2 and VP3 pore-forming activities showed impaired viral infection [46] . These results suggest that VP2 and VP3 are required for the initial infection stage before the uncoating of the viral genome can take place [91] .