Ivy Tech Community College 16

HIV: Structure, Receptors & Replication Cycle

  • Key surface glycoproteins:

    • gp120 (attachment) binds CD4 primary receptor and co-receptors CCR5 or CXCR4.

    • gp41 (fusion) drives viral-host membrane merger.

  • Viral payload: two identical +ssRNA strands within nucleocapsid.

  • Enzymes embedded in one large polyprotein (requires viral protease to cleave):

    • Reverse Transcriptase (RT) – transcribes RNA \to DNA, error-prone, leads to high mutation rate.

    • Integrase – inserts proviral DNA into host genome.

    • Protease – cleaves polyproteins for viral maturation.

  • Life-cycle checkpoints:

    1. Attachment/Binding: gp120 binds CD4 and a co-receptor (CCR5 or CXCR4).

    2. Fusion: gp41 mediates fusion of viral and host membranes.

    3. Entry & Uncoating: Nucleocapsid enters and viral genome is released.

    4. Reverse Transcription: Viral RNA is converted to DNA by RT.

    5. Integration: Viral DNA (provirus) is inserted into host DNA by Integrase.

    6. Transcription/Translation: Host machinery produces viral mRNA and polyproteins.

    7. Assembly & Budding: Immature virions assemble at plasma membrane and bud off.

    8. Protease Cleavage: Protease cleaves polyproteins, leading to mature, infectious HIV particles.