VPU

Vpu is an accessory protein encoded by the HIV-1 virus. Its name stands for Viral Protein U. This small protein, approximately 81 amino acids long, plays two critical roles in the viral life cycle, primarily within infected host cells.

One major function of Vpu is to degrade the host protein CD4. CD4 is a receptor on the surface of immune cells, such as T-helper cells, which HIV uses to enter the cell. However, newly synthesized CD4 molecules inside an infected cell can interfere with the assembly and release of new viral particles. Vpu binds to CD4 and recruits cellular machinery to target it for destruction, thereby facilitating efficient virus production.

The second key role of Vpu is to enhance the release of new virus particles from the infected cell. It achieves this by counteracting tetherin, a host defense protein. Tetherin acts like a tether, physically restraining newly formed virions on the cell surface, preventing them from spreading to other cells. Vpu neutralizes tetherin, allowing the virus particles to be released freely.

Due to its essential functions in promoting viral replication and spread, Vpu is considered a virulence factor. Research into Vpu is significant for understanding HIV pathogenesis and for developing novel antiviral strategies that could target this unique viral protein.