Figure 2 |. Gag structure and functions.

High-resolution structures of the major domains of Gag — matrix (MA), capsid (CA), nucleocapsid (NC) and p6 — are presented over a linear depiction of the Gag precursor polyprotein. The major functions of each Gag domain are indicated. MA (Protein Data Bank (PDB) accession 1HIW)³⁷ is involved in Gag targeting and binding to the plasma membrane, and in incorporation of the envelope (Env) glycoprotein. Membrane binding requires amino-terminal myristylation (Myr). CA (PDB accession 2M8N)¹¹⁵ participates in Gag assembly, formation of the conical capsid core and regulation of the nuclear import of viral DNA. The CA N-terminal domain (CA_NTD) contains an N-terminal β-hairpin and a proline-rich loop that binds the host protein cyclophilin A (CYPA); the CA carboxy-terminal domain (CA_CTD) contains the major homology region (MHR). CA_NTD and CA_ctd are connected by a short, flexible interdomain linker. Spacer peptide 1 (SP1) is involved in Gag assembly. NC (PDB accession 1BJ6)¹¹⁶ contains two zinc-finger domains; it participates in Gag assembly and RNA encapsidation, and serves as an RNA chaperone. p6 (PDB accession 2C55)⁸ is involved in recruitment of the endosomal sorting complex required for transport (ESCRT) components and in Vpr incorporation.