Host cell factors that interact with the HIV capsid and modulate uncoating

The human immunodeficiency virus type 1 (HIV-1) capsid core, which encapsulates the viral RNA genome, is delivered into the target cell cytosol as a result of the virus entry process. In the target cell cytosol, the conical capsid core undergoes morphological changes, and most of the capsid proteins arc disassociated from the viral genome, a process termed uncoating. Although not well understood, proper uncoating appears to be essential for efficient HIV-1 infection.;The capsid-interacting factor rhesus monkey TRIM5alpha has been shown to restrict HIV-1 infection by promoting rapid, premature disassembly of the capsid. Human TRIM5alpha (TRIM5alphahu) only modestly inhibits HIV-1. Alteration of arginine 332 in the TRIM5alphahu B30.2 domain to proline, the residue found in rhesus monkey TRIM5alpha, has been shown to create a potent restricting factor for HIV-1, To investigate the specific sequence requirements for the anti-viral activity of TRIM5alphahu, we generated mutant proteins in which arginine 332 was replaced by different amino acid residues. We found that the potentiation of HIV-1 inhibition resulted from the removal of a positively charged residue at position 332 of TRIM5alpha hu. The increase in restricting activity correlated with an increase in the ability of TRIM5alphahu variants to bind HIV-1 capsid complexes. A change in the cyclophilin A-binding loop of the HIV-1 capsid decreased TRIM5alphahu R332P binding and allowed escape from restriction. Thus, charged residues in the TRIM5alphahu B30.2 domain can modulate capsid binding and restriction potency.;The binding of cyclophilin A (CypA) to the HIV-1 capsid (CA) protein is required soon after virus entry into natural target cells. To understand the role of CypA in HIV-1 infection, we examined the effects of the amino acid changes in the cyclophilin A-binding loop of the HIV-1 CA protein on the stability of capsid complexes assembled in vitro and on capsid disassembly in the cytosol of virus-exposed target cells. An A92E change impaired CA-CA interactions in vitro and decreased the amount of particulate capsids in the cytosol of HeLa target cells. Reducing the binding of CypA the A92E mutant capsid increased the amount of particulate capsids and viral infectivity in HeLa cells. By contrast, reduction of the binding of CypA to HIV-1 capsids in Jurkat T lymphocytes resulted in a decrease in the amount of particulate capsids and infectivity. Thus, depending on the capsid and the target cell, CypA-CA binding either stabilized or destabilized the capsid, indicating that CypA modulates HIV-1 capsid disassembly. These results may suggest new interventional approaches for retroviral infection.