Abstract
HIV-1 Gag protein interaction with cyclophilin A (CypA) is critical for viral fitness. Among the amino acid substitutions identified in Gag noncleavage sites in HIV-1 variants resistant to protease inhibitors, H219Q (Gatanaga, H., Suzuki, Y., Tsang, H., Yoshimura, K., Kavlick, M. F., Nagashima, K., Gorelick, R. J., Mardy, S., Tang, C., Summers, M. F., and Mitsuya, H. (2002) J. Biol. Chem. 277, 5952-5961) and H219P substitutions in the viral CypA binding loop confer the greatest replication advantage to HIV-1. These substitutions represent polymorphic amino acid residues. We found that the replication advantage conferred by these substitutions was far greater in CypA-rich MT-2 and H9 cells than in Jurkat cells and peripheral blood mononuclear cells (PBM), both of which contained less CypA. High intracellular CypA content in H9 and MT-2 cells, resulting in excessive CypA levels in virions, limited wild-type HIV-1 (HIV-1(WT)) replication and H219Q introduction into HIV-1 (HIV-1(H219Q)), reduced CypA incorporation of HIV-1, and potentiated viral replication. H219Q introduction also restored the otherwise compromised replication of HIV-1(P222A) in PBM, although the CypA content in HIV-1(H219Q/P222A) was comparable with that in HIV-1(P222A), suggesting that H219Q affected the conformation of the CypA-binding motif, rendering HIV-1 replicative in a low CypA environment. Structural modeling analyses revealed that although hydrogen bonds are lost with H219Q and H219P substitutions, no significant distortion of the CypA binding loop of Gag occurred. The loop conformation of HIV-1(P222A) was found highly distorted, although H219Q introduction to HIV-1 restored the conformation of the loop close to that of HIV-1 (P222A). The present data suggested that the effect of CypA on HIV-1 replicative (WT) ability is bimodal (both high and low CypA content limits HIV-1 replication), that the conformation of the CypA binding region of Gag is important for viral fitness, and that the function of CypA is to maintain the conformation.
Highlights
Combination antiretroviral therapy has brought about improved quality of life and extended survival in patients with HIV-13 infection
We asked how H219Q and H219P substitutions occurring within the viral cyclophilin A (CypA) binding loop conferred replication advantage to HIV-1, and we examined whether these substitutions affected the conformation and interaction of p24 Gag protein and CypA during HIV-1 propagation in various host cells
In an attempt to corroborate and extend our previous observations and to determine how often such amino acid substitutions develop in the Gag protein, we examined four more HIV-1 variants that were selected in vitro against various protease inhibitors (PIs), including three novel PIs, UIC-00041, UIC-00142, and UIC-00145
Summary
Combination antiretroviral therapy has brought about improved quality of life and extended survival in patients with HIV-13 infection. We asked how H219Q and H219P substitutions occurring within the viral CypA binding loop conferred replication advantage to HIV-1, and we examined whether these substitutions affected the conformation and interaction of p24 Gag protein and CypA during HIV-1 propagation in various host cells.
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