Envelope Glycoprotein Gp130 (env) Feline Foamy Virus Recombinant Protein

Function: The surface protein (SU) attaches the virus to the host cell by binding to the cell receptor. This interaction triggers the refolding of transmembrane protein (TM) and is thought to activate its fusogenic potential by unmasking its fusion peptide

By similarity.The transmembrane protein (TM) acts as a class I viral fusion protein. Under the current model, the protein has at least 3 conformational states: pre-fusion native state, pre-hairpin intermediate state, and post-fusion hairpin state. During viral and target cell membrane fusion, the coiled coil regions (heptad repeats) assume a trimer-of-hairpins structure, positioning the fusion peptide in close proximity to the C-terminal region of the ectodomain. The formation of this structure appears to drive apposition and subsequent fusion of viral and target cell membranes. Membranes fusion leads to delivery of the nucleocapsid into the cytoplasm

By similarity.The leader peptide is a component of released, infectious virions and is required for particle budding.

Subunit structure: The mature envelope protein consists of a trimer of SU-TM heterodimers

By similarity. The N-terminus of leader peptide specifically interacts with Gag protein. This specific interaction between Gag protein and Env glycoprotein may allow particle egress. Ref.3 Ref.4

Subcellular location: Envelope glycoprotein gp130: Host endoplasmic reticulum membrane. Note: The polyprotein has a highly unusual biosynthesis for a retroviral glycoprotein. It is translated as a full-length precursor protein into the rough endoplasmic reticulum and initially has a type III protein configuration with both its N and C-termini located intracytoplasmically. Ref.4Leader peptide: Virion membrane; Single-pass type II membrane protein

Probable. Host endoplasmic reticulum membrane; Single-pass type II membrane protein

Probable. Note: Its N-terminus is located inside the viral particle

By similarity. Ref.4Transmembrane protein: Virion membrane; Single-pass type I membrane protein

Probable. Host endoplasmic reticulum membrane; Single-pass type I membrane protein

Probable Ref.4. Surface protein: Virion membrane; Peripheral membrane protein

By similarity. Host endoplasmic reticulum membrane; Peripheral membrane protein

By similarity. Note: The surface protein is not anchored to the viral envelope, but associates with the extravirion surface through its binding to TM

By similarity. Ref.4

Domain: The ER retention signal plays an important role in establishing the intracellular site of budding

By similarity.

Post-translational modification: Envelope glycoproteins are synthesized as a inactive precursor that is processed by host furin or a furin-like protease to yield a functional hetero-oligomeric complex. A 9 kDa protein corresponding to the N-terminus of the leader peptide may arise through low efficient cleavage by host signal peptidase.The transmembrane protein and the surface protein are N-glycosylated

By similarity.

Miscellaneous: Foamy viruses are distinct from other retroviruses in many respects. Their protease is active as an uncleaved Pro-Pol protein. Mature particles do not include the usual processed retroviral structural protein (MA, CA and NC), but instead contain two large Gag proteins. Their functional nucleic acid appears to be either RNA or dsDNA (up to 20% of extracellular particles), because they probably proceed either to an early (before integration) or late reverse transcription (after assembly). Foamy viruses have the ability to retrotranspose intracellularly with high efficiency. They bud predominantly into the endoplasmic reticulum (ER) and occasionally at the plasma membrane. Budding requires the presence of Env proteins. Most viral particles probably remain within the infected cell.