Demeler, Borries

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Browsing Demeler, Borries by Author "Bhattacharya, Akash"

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    Effects of T592 phosphomimetic mutations on tetramer stability and dNTPase activity of SAMHD1 can not explain the retroviral restriction defect
    (Nature Publishing, 2016) Bhattacharya, Akash; Wang, Zhonghua; White, Tommy; Buffone, Cindy; Nguyen, Laura A.; Shepard, Caitlin N.; Kim, Baek; Demeler, Borries; Diaz-Griffero, Felipe; Ivanov, Dmitri N.
    SAMHD1, a dNTP triphosphohydrolase, contributes to interferon signaling and restriction of retroviral replication. SAMHD1-mediated retroviral restriction is thought to result from the depletion of cellular dNTP pools, but it remains controversial whether the dNTPase activity of SAMHD1 is sufficient for restriction. The restriction ability of SAMHD1 is regulated in cells by phosphorylation on T592. Phosphomimetic mutations of T592 are not restriction competent, but appear intact in their ability to deplete cellular dNTPs. Here we use analytical ultracentrifugation, fluorescence polarization and NMR-based enzymatic assays to investigate the impact of phosphomimetic mutations on SAMHD1 tetramerization and dNTPase activity in vitro. We find that phosphomimetic mutations affect kinetics of tetramer assembly and disassembly, but their effects on tetramerization equilibrium and dNTPase activity are insignificant. In contrast, the Y146S/Y154S dimerization-defective mutant displays a severe dNTPase defect in vitro, but is indistinguishable from WT in its ability to deplete cellular dNTP pools and to restrict HIV replication. Our data suggest that the effect of T592 phosphorylation on SAMHD1 tetramerization is not likely to explain the retroviral restriction defect and we hypothesize that enzymatic activity of SAMHD1 is subject to additional cellular regulatory mechanisms that have not yet been recapitulated in vitro.
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    Functionality of redox-active crysteines is required for restriction of retroviral replication by SAMHD1
    (Cell Press, 2018) Wang, Zhonghua; Bhattacharya, Akash; White, Tommy; Buffone, Cindy; McCabe, Aine; Nguyen, Laura A.; Shepard, Caitlin N.; Pardo, Sammy; Kim, Baek; Weintraub, Susan T.; Demeler, Borries; Diaz-Griffero, Felipe; Ivanov, Dmitri N.
    SAMHD1 is a dNTP triphosphohydrolase (dNTPase)that impairs retroviral replication in a subset of non-cycling immune cells. Here we show that SAMHD1is a redox-sensitive enzyme and identify threeredox-active cysteines within the protein: C341,C350, and C522. The three cysteines reside nearone another and the allosteric nucleotide bindingsite. Mutations C341S and C522S abolish the abilityof SAMHD1 to restrict HIV replication, whereas theC350S mutant remains restriction competent. TheC522S mutation makes the protein resistant to inhibi-tion by hydrogen peroxide but has no effect onthe tetramerization-dependent dNTPase activity ofSAMHD1in vitroor on the ability of SAMHD1 todeplete cellular dNTPs. Our results reveal that enzy-matic activation of SAMHD1 via nucleotide-depen-dent tetramerization is not sufficient for the estab-lishment of the antiviral state and that retroviralrestriction depends on the ability of the protein to un-dergo redox transformations.
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    General model for retroviral capsid pattern recognition by TRIM5 proteins
    (American Society for Microbiology, 2018) Wagner, Jonathan M.; Christensen, Devin E.; Bhattacharya, Akash; Dawidziak, Daria M.; Roganowicz, Marcin D.; Wan, Yueping; Pumroy, Ruth A.; Demeler, Borries; Ivanov, Dmitri N.; Ganser-Pornillos, Barbie K.; Sundquist, Wesley I.; Pornillos, Owen
    Restriction factors are intrinsic cellular defense proteins that have evolved to block microbial infections. Retroviruses such as HIV-1 are restricted by TRIM5 proteins, which recognize the viral capsid shell that surrounds, organizes, and protects the viral genome. TRIM5α uses a SPRY domain to bind capsids with low intrinsic affinity (KD of >1 mM) and therefore requires higher-order assembly into a hexagonal lattice to generate sufficient avidity for productive capsid recognition. TRIMCyp, on the other hand, binds HIV-1 capsids through a cyclophilin A domain, which has a well-defined binding site and higher affinity (KD of ∼10 μM) for isolated capsid subunits. Therefore, it has been argued that TRIMCyp proteins have dispensed with the need for higher-order assembly to function as antiviral factors. Here, we show that, consistent with its high degree of sequence similarity with TRIM5α, the TRIMCyp B-box 2 domain shares the same ability to self-associate and facilitate assembly of a TRIMCyp hexagonal lattice that can wrap about the HIV-1 capsid. We also show that under stringent experimental conditions, TRIMCyp-mediated restriction of HIV-1 is indeed dependent on higher-order assembly. Both forms of TRIM5 therefore use the same mechanism of avidity-driven capsid pattern recognition
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    Nucleic acid binding by SAMHD1 contributes to the antiretroviral activity and is enhanced by the GpsN modification
    (Nature Publishing Group, 2021) Yu, Corey H.; Bhattacharya, Akash; Persaud, Mirjana; Taylor, Alexander B.; Wang, Zhonghua; Bulnes-Ramos, Angel; Xu, Joella; Selyutina, Anastasia; Martinez-Lopez, Alicia; Cano, Kristin; Demeler, Borries; Kim, Baek; Hardies, Stephen C.; Diaz-Griffero, Felipe; Ivanov, Dmitri N.
    SAMHD1 impedes infection of myeloid cells and resting T lymphocytes by retroviruses, and the enzymatic activity of the protein—dephosphorylation of deoxynucleotide triphosphates (dNTPs)—implicates enzymatic dNTP depletion in innate antiviral immunity. Here we show that the allosteric binding sites of the enzyme are plastic and can accommodate oligonucleotides in place of the allosteric activators, GTP and dNTP. SAMHD1 displays a preference for oligonucleotides containing phosphorothioate bonds in the Rp configuration located 3’ to G nucleotides (GpsN), the modification pattern that occurs in a mechanism of antiviral defense in prokaryotes. In the presence of GTP and dNTPs, binding of GpsN-containing oligonucleotides promotes formation of a distinct tetramer with mixed occupancy of the allosteric sites. Mutations that impair formation of the mixed-occupancy complex abolish the antiretroviral activity of SAMHD1, but not its ability to deplete dNTPs. The findings link nucleic acid binding to the antiretroviral activity of SAMHD1, shed light on the immunomodulatory effects of synthetic phosphorothioated oligonucleotides and raise questions about the role of nucleic acid phosphorothioation in human innate immunity.