Abstract
BackgroundHost SAM domain and HD domain-containing protein 1 (SAMHD1) suppresses reverse transcription kinetics of HIV-1 in nondividing cells such as macrophages by hydrolyzing and nearly depleting cellular dNTPs, which are the substrates of viral reverse transcriptase (RT). However, unlike HIV-1, HIV-2 and SIVsm encode viral protein X (Vpx), which counteracts the dNTPase activity of SAMHD1 and elevates dNTP concentration, allowing the viruses to replicate under abundant dNTP conditions even in nondividing cells.FindingsHere we tested whether RTs of these Vpx coding and noncoding lentiviruses display different enzyme kinetic profiles in response to dNTP concentrations. For this test, we characterized an extensive collection of RTs from 7 HIV-1 strains, 4 HIV-2 strains and 7 SIV strains, and determined their steady-state kinetic parameters. The Km values of all HIV-1 RTs were consistently low and close to the low dNTP concentrations found in macrophages. However, the Km values of SIV and HIV-2 RTs were not only higher than those of HIV-1 RTs but also varied significantly, indicating that HIV-2/SIV RTs require higher dNTP concentrations for efficient DNA synthesis, compared to HIV-1 RT. However, the kcat values of all eighteen lentiviral RTs were very similar.ConclusionsOur biochemical analysis supports the hypothesis that the enzymological properties, particularly, Km values, of lentivirus RTs, are mechanistically tied with the cellular dNTP availability in nondividing target cells, which is controlled by SAMHD1 and Vpx.
Highlights
Host SAM domain and HD domain-containing protein 1 (SAMHD1) suppresses reverse transcription kinetics of HIV-1 in nondividing cells such as macrophages by hydrolyzing and nearly depleting cellular dNTPs, which are the substrates of viral reverse transcriptase (RT)
Due to the limited dNTP availability, nondividing macrophages are suboptimal for supporting proviral DNA synthesis of lentiviruses as compared to the activated and constantly dividing CD4+ T cells [2,5]
A series of recent studies showed that the host SAM domain and HD domaincontaining protein 1 (SAMHD1) protein has dNTP hydrolase and RNase activities and serves as a restriction factor that can delay the replication kinetics of lentiviruses [6,7,8,9,10], and the dNTP hydrolase activity of SAMHD1 is responsible for the poor dNTP availability in the viral nondividing target cell types such as macrophages and dendritic cells (DCs) [11]
Summary
Host SAM domain and HD domain-containing protein 1 (SAMHD1) suppresses reverse transcription kinetics of HIV-1 in nondividing cells such as macrophages by hydrolyzing and nearly depleting cellular dNTPs, which are the substrates of viral reverse transcriptase (RT). Due to the limited dNTP availability, nondividing macrophages are suboptimal for supporting proviral DNA synthesis of lentiviruses as compared to the activated and constantly dividing CD4+ T cells [2,5].
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