[Entry process of enveloped viruses to host cells].

The fusion between viral and cellular membranes is the first critical step of the enveloped viral infection. This is promoted by the drastic conformational change of the viral fusion protein. The conformational change is driven by various cues that are different in each fusion protein. The divergent nature of the induction mechanism of fusion proteins tells us that the regulation of membrane fusion process is substantially important to viral infection. Historically, enveloped viruses were categorized into pH-dependent and pH-independent groups for their entry processes. It has been thought that the pH-independent viruses mainly fuse to cell membrane at the cell surface whereas pH-dependent viruses fuse to endosomal membrane. However, the recent studies suggest that some pH-independent viruses including Human Immunodeficiency Virus (HIV) also utilize the endocytosis pathway to achieve infection. In addition, it has been revealed that the host factors other than receptors play crucial roles in the entry of enveloped viruses. This review summarizes the entry process of enveloped viruses and focuses on the current topics of HIV entry.