The viral envelope is a lipid bilayer derived from the host cell membrane and studded with virus encoded proteins. It surrounds the nucleocapsid of many animal viruses and protects the genetic material while facilitating entry into host cells. Viral membrane proteins bind to host receptors and promote fusion between the viral and cellular membranes.
Structure and assembly
Enveloped viruses use host lipids to construct a membrane around their nucleocapsid. Depending on the virus, the lipid bilayer is obtained from the plasma membrane, endoplasmic reticulum, Golgi apparatus or nuclear membrane during budding. The envelope contains lipids from the host but is populated almost exclusively by viral transmembrane glycoproteins. These glycoproteins mediate attachment to cellular receptors and catalyze membrane fusion, allowing the viral core to enter the cytoplasm. Because the envelope is derived from the host, it is flexible and non‑rigid, enabling enveloped viruses to exit by budding without lysing the cell. The presence of a lipid membrane distinguishes enveloped viruses from non‑enveloped ones, which have only a protein coat. Viral envelopes confer sensitivity to detergents, solvents and desiccation, meaning these viruses often require direct transmission between hosts.
Notable examples and considerations
Enveloped viruses occur across many families, including orthomyxoviruses, retroviruses, coronaviruses, bunyaviruses and herpesviruses. Influenza viruses bud from the plasma membrane and display hemagglutinin and neuraminidase glycoproteins that mediate receptor binding and membrane fusion. Coronaviruses assemble in the endoplasmic reticulum–Golgi intermediate compartment, while bunyaviruses bud from the Golgi and herpesviruses from the nuclear envelope. Human immunodeficiency virus (HIV) uses envelope glycoproteins gp120 and gp41 to recognize CD4 and co receptors on T cells and fuse with the cell membrane. Because the envelope is host‑derived, some viruses incorporate host proteins into it, aiding immune evasion. The lipid envelope makes these viruses sensitive to alcohol‑based disinfectants and environmental drying, whereas non‑enveloped viruses such as adenoviruses are more resistant.
The envelope is a key determinant of viral infectivity and stability. By combining host‑derived lipids with specialized viral glycoproteins, the membrane protects the nucleocapsid and mediates cell entry. Understanding envelope composition helps in developing antiviral agents and vaccines that target fusion proteins and block budding.
Related Terms: Nucleocapsid, Capsid, Glycoprotein, Budding, Viral membrane