Glycoproteins on the Protein Coat of Virus

The protein coat of a virus, also known as the viral envelope, plays a crucial role in the attachment and entry of the virus into host cells. Glycoproteins present on the protein coat are responsible for facilitating this process. Among the given options, GP120 is the glycoprotein that helps in the attachment of the virus to CD4 receptors.

GP120: The Key Glycoprotein

GP120 is a glycoprotein found on the outer envelope of the human immunodeficiency virus (HIV). It is primarily responsible for the attachment of the virus to the CD4 receptors present on the surface of host immune cells, particularly helper T cells.

Role of GP120 in Virus Attachment

1. Recognition and Binding: GP120 acts as a receptor-binding protein that recognizes and binds to the CD4 receptors on the surface of host cells. This initial attachment is the first step in the infection process.

2. Co-Receptor Interaction: After GP120 binds to CD4, it undergoes conformational changes that allow it to interact with a co-receptor, typically either CCR5 or CXCR4. This interaction further stabilizes the attachment of the virus to the host cell.

3. Membrane Fusion: The binding of GP120 to both CD4 and a co-receptor triggers a series of events that lead to membrane fusion between the viral envelope and the host cell membrane. This fusion allows the viral contents to enter the host cell.

4. Viral Entry: Once the viral envelope fuses with the host cell membrane, the viral RNA and other components are released into the host cell cytoplasm, initiating the viral replication process.

Conclusion

Among the given options, GP120 is the glycoprotein on the protein coat of the virus that helps in the attachment of the virus to CD4 receptors. Through its interaction with CD4 and co-receptors, GP120 facilitates the recognition, binding, and entry of the virus into host cells. Understanding the role of glycoproteins like GP120 is important for developing strategies to prevent viral attachment and subsequent infection.