2 copies of single stranded RNA. Nucleocapsid protein 7 is in close association with the RNA and participates in its replication.
Three critical replication enzymes: reverse transcriptase, integrase, and protease.
Capsid comprises protein 24.
Matrix comprises protein 17.
Viral envelope comprises a lipid bilayer; as we'll see, this outer membrane was derived from the host cell's membrane.
The outer surface of the virion is covered by envelope glycoproteins (sometimes referred to as "envelope spikes"):
Gp41 spans the membrane; Gp120 is the proximal tip.
HIV shares structural genes with other retroviruses:
Pol codes for the large protein precursors of reverse transcriptase, integrase, and protease (each of which is cleaved by protease).
Gag codes for matrix, capsid, and nucleocapsid proteins.
Env codes for the envelope proteins that give rise to glycoproteins 41 and 120.
Key Targets of HIV Virion
Recall that HIV most commonly enters the hosts' body via mucosal tissues; not surprisingly, the following cell types are prevalent in mucosa:
Activated CD4+ T cells, which comprise the Helper T cell lineage of the adaptive immune system. Recall that depletion of CD4+ T cells key to the pathogenesis of HIV, as it leads to severe immunosuppression.
CD4+ T cells can have CCR5 or CXCR4 co-receptors.
Though there is great intertextual variation on this point, co-receptor expression and, therefore, susceptibility to R5 or X4 HIV strains may depend on their developmental and/or activation status.
Furthermore, naïve T cells are "protected" by the enzyme APOBEC3G, which inhibits viral replication; however, upon activation, this enzyme is converted and no longer prevents replication.
Unfortunately, protection can be counteracted by Vif (viral infectivity factor), which is an HIV accessory protein that degrades APOBEC3G.
Dendritic cells display CCR5 co-receptors as well as DC-SIGN lectin receptors; not only are some types of dendritic cells susceptible to HIV infection, they also carry HIV transmission to T cells.
Macrophages display CCR5 co-receptors; macrophages may be infected, carry HIV to T cells, or they may serve as viral reservoirs, facilitating HIV's evasion of host immune responses.
