I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[18566]
Open Access
Abstract: Zinc finger antiviral protein (ZAP) is a cytoplasmic protein central to host innate immunity to viral infection. ZAP has no intrinsic catalytic activity but inhibits viral replication by binding to CpG dinucleotides in cytoplasmic viral RNA and recruiting other factors to inhibit protein synthesis and target the RNA for degradation. KHNYN is a ZAP-binding protein required for ZAP-restriction of CpG-rich viral genomes. It contains an extended diKH, PIN nuclease, and CUElike domain, each of which are required for ZAP restriction of viral replication. Here, we report a structural, enzymological, and virological study of KHNYN’s essential PIN nuclease domain. Our crystal structure reveals an extended PIN domain (ex-PIN) containing a conserved N-terminal arm region required for domain stability and an active site tetra-Asp motif, which are both required for antiviral activity. Unlike the weak activity recently reported for the PIN domain, we demonstrate that the KHNYN ex-PIN domain is a highly active Mn2+-dependent single-stranded RNA endonuclease that cleaves with a preference for ApC, ApA, and UpA dinucleotides. These observations extend our view of KHNYN antiviral activity and suggest an unforeseen role for activation by manganese ions in the ZAP–KHNYN antiviral response.
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Dec 2025
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I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
I24-Microfocus Macromolecular Crystallography
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Diamond Proposal Number(s):
[25587]
Open Access
Abstract: The evolutionary history of retrotransposons and their hosts shapes the dynamics of transposition and restriction. The Pseudoviridae of yeast includes multiple Ty1 LTR-retrotransposon subfamilies. Saccharomyces cerevisiae prevents uncontrolled retrotransposition of Ty1 subfamilies using distinct mechanisms: canonical Ty1 is inhibited by a self-encoded restriction factor, p22/p18, whereas Ty1’ is inhibited by an endogenized restriction factor, Drt2. The minimal inhibitory fragment of both restriction factors (p18m and Drt2m) is a conserved C-terminal capsid domain. Here, we use biophysical and genetic approaches to demonstrate that p18m and Drt2m are highly specific to their subfamilies. Although the crystal structures of p18m and Drt2m are similar, three divergent residues found in a conserved hydrophobic interface direct restriction specificity. By mutating these three residues, we re-target each restriction factor to the opposite transposon. Our work highlights how a common lattice-poisoning mechanism of restriction evolved from independent evolutionary trajectories in closely related retrotransposon subfamilies. These data raise the possibility that similar capsid-capsid interactions may exist in other transposons/viruses and that highly specific inhibitors could be engineered to target capsid interfaces.
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Oct 2025
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I04-Macromolecular Crystallography
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Rebecca L.
Youle
,
María José
Lista
,
Clement
Bouton
,
Simone
Kunzelmann
,
Harry
Wilson
,
Matthew A.
Cottee
,
Andrew G.
Purkiss
,
Elizabeth R.
Morris
,
Stuart J. D.
Neil
,
Ian A.
Taylor
,
Chad M.
Swanson
Diamond Proposal Number(s):
[25587]
Open Access
Abstract: Zinc finger antiviral protein (ZAP) binds CpG dinucleotides in viral RNA and targets them for decay. ZAP interacts with several cofactors to form the ZAP antiviral system, including KHNYN, a multidomain endoribonuclease required for ZAP-mediated RNA decay. However, it is unclear how the individual domains in KHNYN contribute to its activity. Here, we demonstrate that the KHNYN amino terminal extended-diKH (ex-diKH) domain is required for antiviral activity and present its crystal structure. The structure belongs to a rare group of KH-containing domains, characterized by a non-canonical arrangement between two type-1 KH modules, with an additional helical bundle. N4BP1 is a KHNYN paralog with an ex-diKH domain that functionally complements the KHNYN ex-diKH domain. Interestingly, the ex-diKH domain structure is present in N4BP1-like proteins in lancelets, which are basal chordates, indicating that it is evolutionarily ancient. While many KH domains demonstrate RNA binding activity, biolayer interferometry and electrophoretic mobility shift assays indicate that the KHNYN ex-diKH domain does not bind RNA. Furthermore, residues required for canonical KH domains to bind RNA are not required for KHNYN antiviral activity. By contrast, an inter-KH domain cleft in KHNYN is a potential protein-protein interaction site and mutations that eliminate arginine salt bridges at the edge of this cleft decrease KHNYN antiviral activity. This suggests that this domain could be a binding site for an unknown KHNYN cofactor.
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Feb 2025
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I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
I24-Microfocus Macromolecular Crystallography
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Diamond Proposal Number(s):
[25587]
Open Access
Abstract: Poly(ADP-ribose) polymerase (PARP) inhibitors are used in the clinic to treat BRCA-deficient breast, ovarian and prostate cancers. As their efficacy is potentiated by loss of the nucleotide salvage factor DNPH1 there is considerable interest in the development of highly specific small molecule DNPH1 inhibitors. Here, we present X-ray crystal structures of dimeric DNPH1 bound to its substrate hydroxymethyl deoxyuridine monophosphate (hmdUMP). Direct interaction with the hydroxymethyl group is important for substrate positioning, while conserved residues surrounding the base facilitate target discrimination. Glycosidic bond cleavage is driven by a conserved catalytic triad and proceeds via a two-step mechanism involving formation and subsequent disruption of a covalent glycosyl-enzyme intermediate. Mutation of a previously uncharacterised yet conserved glutamate traps the intermediate in the active site, demonstrating its role in the hydrolytic step. These observations define the enzyme’s catalytic site and mechanism of hydrolysis, and provide important insights for inhibitor discovery.
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Oct 2023
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I04-Macromolecular Crystallography
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Matthew
Singer
,
Tung
Dinh
,
Lev
Levintov
,
Arun S.
Annamalai
,
Juan S.
Rey
,
Lorenzo
Briganti
,
Nicola J.
Cook
,
Valerie E.
Pye
,
Ian A.
Taylor
,
Kyungjin
Kim
,
Alan N.
Engelman
,
Baek
Kim
,
Juan R.
Perilla
,
Mamuka
Kvaratskhelia
,
Peter
Cherepanov
Diamond Proposal Number(s):
[13775]
Open Access
Abstract: Allosteric HIV-1 integrase (IN) inhibitors (ALLINIs) are an emerging class of small molecules that disrupt viral maturation by inducing the aberrant multimerization of IN. Here, we present cocrystal structures of HIV-1 IN with two potent ALLINIs, namely, BI-D and the drug candidate Pirmitegravir. The structures reveal atomistic details of the ALLINI-induced interface between the HIV-1 IN catalytic core and carboxyl-terminal domains (CCD and CTD). Projecting from their principal binding pocket on the IN CCD dimer, the compounds act as molecular glue by engaging a triad of invariant HIV-1 IN CTD residues, namely, Tyr226, Trp235, and Lys266, to nucleate the CTD-CCD interaction. The drug-induced interface involves the CTD SH3-like fold and extends to the beginning of the IN carboxyl-terminal tail region. We show that mutations of HIV-1 IN CTD residues that participate in the interface with the CCD greatly reduce the IN-aggregation properties of Pirmitegravir. Our results explain the mechanism of the ALLINI-induced condensation of HIV-1 IN and provide a reliable template for the rational development of this series of antiretrovirals through the optimization of their key contacts with the viral target.
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Feb 2023
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I24-Microfocus Macromolecular Crystallography
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Diamond Proposal Number(s):
[13775]
Open Access
Abstract: Solution and solid-state NMR spectroscopy are highly complementary techniques for studying structure and dynamics in very high molecular weight systems. Here we have analysed the dynamics of HIV-1 capsid (CA) assemblies in presence of the cofactors IP6 and ATPγS and the host-factor CPSF6 using a combination of solution state and cross polarisation magic angle spinning (CP-MAS) solid-state NMR. In particular, dynamical effects on ns to µs and µs to ms timescales are observed revealing diverse motions in assembled CA.
Using CP-MAS NMR, we exploited the sensitivity of the amide/Cα-Cβ backbone chemical shifts in DARR and NCA spectra to observe the plasticity of the HIV-1 CA tubular assemblies and also map the binding of cofactors and the dynamics of cofactor-CA complexes. In solution, we measured how the addition of host- and co-factors to CA -hexamers perturbed the chemical shifts and relaxation properties of CA-Ile and -Met methyl groups using transverse-relaxation-optimized NMR spectroscopy to exploit the sensitivity of methyl groups as probes in high-molecular weight proteins. These data show how dynamics of the CA protein assembly over a range of spatial and temporal scales play a critical role in CA function. Moreover, we show that binding of IP6, ATPγS and CPSF6 results in local chemical shift as well as dynamic changes for a significant, contiguous portion of CA, highlighting how allosteric pathways communicate ligand interactions between adjacent CA protomers.
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Jun 2022
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I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[13775]
Open Access
Abstract: Excessive replication of Saccharomyces cerevisiae Ty1 retrotransposons is regulated by Copy Number Control, a process requiring the p22/p18 protein produced from a sub-genomic transcript initiated within Ty1 GAG. In retrotransposition, Gag performs the capsid functions required for replication and re-integration. To minimize genomic damage, p22/p18 interrupts virus-like particle function by interaction with Gag. Here, we present structural, biophysical and genetic analyses of p18m, a minimal fragment of Gag that restricts transposition. The 2.8 Å crystal structure of p18m reveals an all α-helical protein related to mammalian and insect ARC proteins. p18m retains the capacity to dimerise in solution and the crystal structures reveal two exclusive dimer interfaces. We probe our findings through biophysical analysis of interface mutants as well as Ty1 transposition and p18m restriction in vivo. Our data provide insight into Ty1 Gag structure and suggest how p22/p18 might function in restriction through a blocking-of-assembly mechanism.
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Sep 2021
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I04-Macromolecular Crystallography
Krios I-Titan Krios I at Diamond
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Sofia
Banchenko
,
Ferdinand
Krupp
,
Christine
Gotthold
,
Jörg
Bürger
,
Andrea
Graziadei
,
Francis
O'Reilly
,
Ludwig
Sinn
,
Olga
Ruda
,
Juri
Rappsilber
,
Christian M. T.
Spahn
,
Thorsten
Mielke
,
Ian A.
Taylor
,
David
Schwefel
Open Access
Abstract: Viruses have evolved means to manipulate the host’s ubiquitin-proteasome system, in order to down-regulate antiviral host factors. The Vpx/Vpr family of lentiviral accessory proteins usurp the substrate receptor DCAF1 of host Cullin4-RING ligases (CRL4), a family of modular ubiquitin ligases involved in DNA replication, DNA repair and cell cycle regulation. CRL4DCAF1 specificity modulation by Vpx and Vpr from certain simian immunodeficiency viruses (SIV) leads to recruitment, poly-ubiquitylation and subsequent proteasomal degradation of the host restriction factor SAMHD1, resulting in enhanced virus replication in differentiated cells. To unravel the mechanism of SIV Vpr-induced SAMHD1 ubiquitylation, we conducted integrative biochemical and structural analyses of the Vpr protein from SIVs infecting Cercopithecus cephus (SIVmus). X-ray crystallography reveals commonalities between SIVmus Vpr and other members of the Vpx/Vpr family with regard to DCAF1 interaction, while cryo-electron microscopy and cross-linking mass spectrometry highlight a divergent molecular mechanism of SAMHD1 recruitment. In addition, these studies demonstrate how SIVmus Vpr exploits the dynamic architecture of the multi-subunit CRL4DCAF1 assembly to optimise SAMHD1 ubiquitylation. Together, the present work provides detailed molecular insight into variability and species-specificity of the evolutionary arms race between host SAMHD1 restriction and lentiviral counteraction through Vpx/Vpr proteins.
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Aug 2021
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I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[13775]
Open Access
Abstract: SAMHD1 is a fundamental regulator of cellular dNTPs that catalyzes their hydrolysis into 2′-deoxynucleoside and triphosphate, restricting the replication of viruses, including HIV-1, in CD4+ myeloid lineage and resting T-cells. SAMHD1 mutations are associated with the autoimmune disease Aicardi-Goutières syndrome (AGS) and certain cancers. More recently, SAMHD1 has been linked to anticancer drug resistance and the suppression of the interferon response to cytosolic nucleic acids after DNA damage. Here, we probe dNTP hydrolysis and inhibition of SAMHD1 using the Rp and Sp diastereomers of dNTPαS nucleotides. Our biochemical and enzymological data show that the α-phosphorothioate substitution in Sp-dNTPαS but not Rp-dNTPαS diastereomers prevents Mg2+ ion coordination at both the allosteric and catalytic sites, rendering SAMHD1 unable to form stable, catalytically active homotetramers or hydrolyze substrate dNTPs at the catalytic site. Furthermore, we find that Sp-dNTPαS diastereomers competitively inhibit dNTP hydrolysis, while Rp-dNTPαS nucleotides stabilize tetramerization and are hydrolyzed with similar kinetic parameters to cognate dNTPs. For the first time, we present a cocrystal structure of SAMHD1 with a substrate, Rp-dGTPαS, in which an Fe–Mg-bridging water species is poised for nucleophilic attack on the Pα. We conclude that it is the incompatibility of Mg2+, a hard Lewis acid, and the α-phosphorothioate thiol, a soft Lewis base, that prevents the Sp-dNTPαS nucleotides coordinating in a catalytically productive conformation. On the basis of these data, we present a model for SAMHD1 stereospecific hydrolysis of Rp-dNTPαS nucleotides and for a mode of competitive inhibition by Sp-dNTPαS nucleotides that competes with formation of the enzyme–substrate complex.
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May 2021
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I03-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
I04-Macromolecular Crystallography
I24-Microfocus Macromolecular Crystallography
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Diamond Proposal Number(s):
[13775, 18566]
Open Access
Abstract: SAMHD1 regulates cellular 2′-deoxynucleoside-5′-triphosphate (dNTP) homeostasis by catalysing the hydrolysis of dNTPs into 2′-deoxynucleosides and triphosphate. In CD4+ myeloid lineage and resting T-cells, SAMHD1 blocks HIV-1 and other viral infections by depletion of the dNTP pool to a level that cannot support replication. SAMHD1 mutations are associated with the autoimmune disease Aicardi–Goutières syndrome and hypermutated cancers. Furthermore, SAMHD1 sensitises cancer cells to nucleoside-analogue anti-cancer therapies and is linked with DNA repair and suppression of the interferon response to cytosolic nucleic acids. Nevertheless, despite its requirement in these processes, the fundamental mechanism of SAMHD1-catalysed dNTP hydrolysis remained unknown. Here, we present structural and enzymological data showing that SAMHD1 utilises an active site, bi-metallic iron-magnesium centre that positions a hydroxide nucleophile in-line with the Pα-O5′ bond to catalyse phosphoester bond hydrolysis. This precise molecular mechanism for SAMHD1 catalysis, reveals how SAMHD1 down-regulates cellular dNTP and modulates the efficacy of nucleoside-based anti-cancer and anti-viral therapies.
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Jun 2020
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