For most retroviruses, including HIV, association with the plasma membrane (PM) promotes the assembly of immature particles, which occurs simultaneously with budding and maturation. In these viruses, maturation is initiated by oligomerization of polyprotein precursors. In contrast, several retroviruses, such as Mason-Pfizer monkey virus (M-PMV), assemble in the cytoplasm into immature particles that are transported across the PM. Therefore, protease activation and specific cleavage must not occur until the pre-assembled particle interacts with the PM. This interaction is triggered by a bipartite signal consisting of a cluster of basic residues in the matrix (MA) domain of Gag polyprotein and a myristoyl moiety N-terminally attached to MA. Here, we provide evidence that myristoyl exposure from the MA core and its insertion into the PM occurs in M-PMV. By a combination of experimental methods, we show that this results in a structural change at the C-terminus of MA allowing efficient cleavage of MA from the downstream region of Gag. This suggests that, in addition to the known effect of the myristoyl switch of HIV-1 MA on the multimerization state of Gag and particle assembly, the myristoyl switch may have a regulatory role in initiating sequential cleavage of M-PMV Gag in immature particles.

• Keywords
• betaretrovirus, infectious disease, matrix protein, maturation, microbiology, myristoyl switch, protease, viruses,
• MeSH
• Cell Membrane MeSH
• Endopeptidases MeSH
• Gene Products, gag chemistry   MeSH
• Mason-Pfizer monkey virus * chemistry   physiology   MeSH
• Proteins MeSH
• Virus Assembly MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Endopeptidases MeSH
• Gene Products, gag MeSH
• Proteins MeSH

Retroviral Gag polyproteins are targeted to the inner leaflet of the plasma membrane through their N-terminal matrix (MA) domain. Because retroviruses of different morphogenetic types assemble their immature particles in distinct regions of the host cell, the mechanism of MA-mediated plasma membrane targeting differs among distinct retroviral morphogenetic types. Here, we focused on possible mechanistic differences of the MA-mediated plasma membrane targeting of the B-type mouse mammary tumor virus (MMTV) and C-type HIV-1, which assemble in the cytoplasm and at the plasma membrane, respectively. Molecular dynamics simulations, together with surface mapping, indicated that, similarly to HIV-1, MMTV uses a myristic switch to anchor the MA to the membrane and electrostatically interacts with phosphatidylinositol 4,5-bisphosphate to stabilize MA orientation. We observed that the affinity of MMTV MA to the membrane is lower than that of HIV-1 MA, possibly related to their different topologies and the number of basic residues in the highly basic MA region. The latter probably reflects the requirement of C-type retroviruses for tighter membrane binding, essential for assembly, unlike for D/B-type retroviruses, which assemble in the cytoplasm. A comparison of the membrane topology of the HIV-1 MA, using the surface-mapping method and molecular dynamics simulations, revealed that the residues at the HIV-1 MA C terminus help stabilize protein-protein interactions within the HIV-1 MA lattice at the plasma membrane. In summary, HIV-1 and MMTV share common features such as membrane binding of the MA via hydrophobic interactions and exhibit several differences, including lower membrane affinity of MMTV MA.

• Keywords
• Gag polyprotein, HIV-1, coarse-grained molecular dynamics, covalent labeling–mass spectrometry, human immunodeficiency virus (HIV), lipid–protein interaction, mass spectrometry (MS), matrix protein, membrane binding, molecular dynamics, mouse mammary tumor virus (MMTV), particle assembly, retrovirus, viral replication,
• MeSH
• Cell Membrane metabolism   pathology   MeSH
• HIV Infections metabolism   pathology   MeSH
• HIV-1 physiology   MeSH
• Tumor Virus Infections metabolism   pathology   MeSH
• Host-Pathogen Interactions MeSH
• Humans MeSH
• Models, Molecular MeSH
• Mice MeSH
• Retroviridae Infections metabolism   pathology   MeSH
• Virus Assembly MeSH
• Mammary Tumor Virus, Mouse physiology   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH