How Viruses Hijack Endocytic Machinery
https://www.nature.com/scitable/topicpage/how-viruses-hijack-endocytic-machinery-14364991/
.....The first step for a virus to invade a cell is to cross the cell's plasma membrane, which is a lipid barrier. In general, a virus consists of one or more layers of protein that enclose its viral genome. In some cases, the virus also contains enzymes, such as polymerases and proteases, which are necessary for viral replication inside the cell. Some viruses also have a lipid envelope embedded with proteins. Both enveloped and nonenveloped viruses use the proteins present on their surfaces to bind to and enter the host cell. Helenius's research showed that viruses have evolved the ability to efficiently hijack and use the cell's endocytosis mechanism to invade their host cells. The endocytic vesicles transport the incoming viral particles from the plasma membrane to the perinuclear area of the host cell, where the conditions for viral replication are optimal.
At that time, scientists knew that endosomal vesicles mature during their trip into the cell and that the pH of the vesicle's lumen gradually decreases. In their studies of SFV, Helenius and his colleagues made a second discovery. They observed that the decrease in the vesicle's pH induced conformational changes in the SFV viral particles (virions), allowing them to escape from the vesicle and enter the cell's cytoplasm, where they could begin their replication cycle....