An updated advancement of bifunctional IL-27 in inflammatory autoimmune diseases.

Interleukin-27 (IL-27) is a member of the IL-12 family. The gene encoding IL-27 is located at chromosome 16p11. IL-27 is considered as a heterodimeric cytokine, which consists of Epstein-Barr virus (EBV)-induced gene 3 (Ebi3) and IL-27p28. Based on the function of IL-27, it binds to receptor IL-27rα or gp130 and then regulates downstream cascade. To date, findings show that the expression of IL-27 is abnormal in different inflammatory autoimmune diseases (including systemic lupus erythematosus, rheumatoid arthritis, Sjogren syndrome, Behcet's disease, inflammatory bowel disease, multiple sclerosis, systemic sclerosis, type 1 diabetes, Vogt-Koyanagi-Harada, and ankylosing spondylitis). Moreover, in vivo and in vitro studies demonstrated that IL-27 is significantly in3volved in the development of these diseases by regulating innate and adaptive immune responses, playing either an anti-inflammatory or a pro-inflammatory role. In this review, we comprehensively summarized information about IL-27 and autoimmunity based on available evidence. It is hoped that targeting IL-27 will hold great promise in the treatment of inflammatory autoimmune disorders in the future.

[Analysis of dissatisfaction and related factors following total hip arthroplasty in patients with Crowe type â ¢-â £ developmental dysplasia of the hip].

OBJECTIVE: To investigate the satisfaction of patients with Crowe Ⅲ-Ⅳ developmental dysplasia of the hip(DDH) after total hip arthroplasty and the related factors. METHODS: A retrospective study included 169 patients with Crowe type Ⅲ-Ⅳ DDH who underwent total hip arthroplasty between March 2013 and March 2018. Patients were surveyed through WeChat, covering overall satisfaction with the operation, satisfaction with ten daily functions, and the top five questions perceived to have a great impact on daily life. Preoperative and postoperative hip function was evaluated by Harris score. RESULTS: One hundred and forty-five questionnaires were received, with a follow-up period ranging from 1 to 5 years with an average of (3.23±1.22) years. Among these patients, 118 patients were satisfied with the surgical outcomes, while 27 patients were dissatisfied, with the overall satisfaction rate of 81.38%(118/145). The top five problems affecting patient life were postoperative hip pain, limb length discrepancy, walking, stair climbing, and squatting. There were no statistical differences in age, sex, body mass index, preoperative Harris scores (P>0.05). However, the dissatisfied group had lower postoperative Harris scores. Postoperative hip pain and limb length discrepancy were identified as direct factors contributing to postoperative surgical dissatisfaction. CONCLUSION: Total hip arthroplasty for patients with Crowe type Ⅲ-Ⅳ DDH is challenging. Postoperative hip pain (mild or severe) and limb length discrepancy (>2 cm) are independent risk factors for postoperative dissatisfaction.

Lupus nephritis or not? A simple and clinically friendly machine learning pipeline to help diagnosis of lupus nephritis.

OBJECTIVE: Diagnosis of lupus nephritis (LN) is a complex process, which usually requires renal biopsy. We aim to establish a machine learning pipeline to help diagnosis of LN. METHODS: A cohort of 681 systemic lupus erythematosus (SLE) patients without LN and 786 SLE patients with LN was established, and a total of 95 clinical, laboratory data and 17 meteorological indicators were collected. After tenfold cross-validation, the patients were divided into training set and test set. The features selected by collective feature selection method of mutual information (MI) and multisurf were used to construct the models of logistic regression, decision tree, random forest, naive Bayes, support vector machine (SVM), light gradient boosting (LGB), extreme gradient boosting (XGB), and artificial neural network (ANN), the models were compared and verified in post-analysis. RESULTS: Collective feature selection method screens out antistreptolysin (ASO), retinol binding protein (RBP), lupus anticoagulant 1 (LA1), LA2, proteinuria and other features, and the hyperparameter optimized XGB (ROC: AUC = 0.995; PRC: AUC = 1.000, APS = 1.000; balance accuracy: 0.990) has the best performance, followed by LGB (ROC: AUC = 0.992; PRC: AUC = 0.997, APS = 0.977; balance accuracy: 0.957). The worst performance is naive Bayes model (ROC: AUC = 0.799; PRC: AUC = 0.822, APS = 0.823; balance accuracy: 0.693). In the composite feature importance bar plots, ASO, RF, Up/Ucr, and other features play important roles in LN. CONCLUSION: We developed and validated a new and simple machine learning pathway for diagnosis of LN, especially the XGB model based on ASO, LA1, LA2, proteinuria, and other features screened out by collective feature selection.

NLRP6 self-assembles into a linear molecular platform following LPS binding and ATP stimulation.

NOD-like receptors (NLRs) localize in the cytosol to recognize intracellular pathogen products and initialize the innate immune response. However, the ligands and ligand specificity of many NLRs remain unclear. One such NLR, NLRP6, plays an important role in maintaining intestinal homeostasis and protecting against various intestinal diseases such as colitis and intestinal tumorigenesis. Here, we show that the major component of the outer membrane of gram-negative bacteria, lipopolysaccharide (LPS), binds NLRP6 directly and induces global conformational change and dimerization. Following stimulation by ATP, the NLRP6 homodimer can further assemble into a linear molecular platform, and ASC is recruited to form higher molecular structures, indicative of a step-by-step activation mechanism. Our study sheds light on the mystery of LPS-induced inflammasome initiation, reveals the architecture and structural basis of potential pre-inflammasome, and suggests a novel molecular assembly pattern for immune receptors.

Meroterpene-like compounds derived from ß-caryophyllene as potent α-glucosidase inhibitors.

Meroterpenoids isolated from guava (Psidium guajava) and Rhodomyrtus tomentosa possess special skeletons which incorporate terpenoids with phloroglucinol derivatives. Most of these meroterpenoids showed high cytotoxicity against cancer cell lines. However, their chemical diversity is very limited. Herein, we employed a biomimetic hetero-cycloaddition starting from ortho-quinone methides and an abundant natural product, ß-caryophyllene, to generate meroterpene-like compounds. Considering that the source plant has hyperglycemic functions, α-glucosidase was selected as a target for bioassay. Nine compounds were screened out for promising activities (IC50 < 15 µM), which were better than the positive controls genistein and acarbose. The best inhibitor 12 (IC50 2.73 µM) possesses two caryophyllene moieties. They represented a new type of skeleton possessing activities against α-glucosidase. The kinetic study exhibited that these inhibitors belong to a non-competitive type. All these inhibitors may provide an opportunity to develop a new class of antidiabetic agents.

Biomarkers and potential pathogenesis of colorectal cancer-related ischemic stroke.

AIM: To investigate the specific biomarkers and potential pathogenesis of colorectal cancer-related ischemic stroke (CRCIS). METHODS: A retrospective study was conducted on CRCIS patients (colorectal cancer patients with ischemic stroke without conventional stroke risk factors) registered at seven centers between January 2007 and December 2017. Clinical data and laboratory and imaging findings were compared with age- and sex- matched patients with colorectal cancer (CRC) without ischemic stroke that were admitted to the same hospital during the same period. Univariate and multivariate analyses were performed to analyze the independent risk factors for CRCIS. A receiver operator characteristic curve was configured to calculate the optimal cut-off value of the products of the independent risk factors for CRCIS. RESULTS: A total of 114 CRCIS patients and 114 CRC patients were included. Multiple lesions in multiple vascular territories were common in CRCIS patients (71, 62.28%). The levels of plasma D-dimer, carcinoembryonic antigen (CEA), cancer antigen 125, and neutrophil count were significantly higher in CRCIS patients than in CRC patients. Multiple logistic regression analysis revealed that plasma D-dimer levels [odds ratio (OR) = 1.002, 95% confidence interval (CI): 1.001-1.003, P < 0.001], CEA levels (OR = 1.011, 95%CI: 1.006-1.015, P < 0.001), and neutrophil count levels (OR = 1.626, 95%CI: 1.268-2.087, P < 0.001) were independent risk factors for CRCIS. In addition, receiver operator characteristic curve revealed that the area under curve for the products of plasma D-dimer, CEA, and neutrophil count was 0.889 ± 0.022 (95%CI: 0.847-0.932, P < 0.001), and the optimal cut-off value for the product was 252.06, which was called the CRCIS Index, with a sensitivity of 86.0% and specificity of 79.8%. CONCLUSION: Hypercoagulability induced by elevated CEA and neutrophils may be an important cause of CRCIS. The CRCIS index, which serves as a biomarker of CRCIS, needs further study.

Alpha-kinase 1 is a cytosolic innate immune receptor for bacterial ADP-heptose.

Immune recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors often activates proinflammatory NF-κB signalling1. Recent studies indicate that the bacterial metabolite D-glycero-ß-D-manno-heptose 1,7-bisphosphate (HBP) can activate NF-κB signalling in host cytosol2-4, but it is unclear whether HBP is a genuine PAMP and the cognate pattern recognition receptor has not been identified. Here we combined a transposon screen in Yersinia pseudotuberculosis with biochemical analyses and identified ADP-ß-D-manno-heptose (ADP-Hep), which mediates type III secretion system-dependent NF-κB activation and cytokine expression. ADP-Hep, but not other heptose metabolites, could enter host cytosol to activate NF-κB. A CRISPR-Cas9 screen showed that activation of NF-κB by ADP-Hep involves an ALPK1 (alpha-kinase 1)-TIFA (TRAF-interacting protein with forkhead-associated domain) axis. ADP-Hep directly binds the N-terminal domain of ALPK1, stimulating its kinase domain to phosphorylate and activate TIFA. The crystal structure of the N-terminal domain of ALPK1 and ADP-Hep in complex revealed the atomic mechanism of this ligand-receptor recognition process. HBP was transformed by host adenylyltransferases into ADP-heptose 7-P, which could activate ALPK1 to a lesser extent than ADP-Hep. ADP-Hep (but not HBP) alone or during bacterial infection induced Alpk1-dependent inflammation in mice. Our findings identify ALPK1 and ADP-Hep as a pattern recognition receptor and an effective immunomodulator, respectively.

The C2'- and C3'-endo equilibrium for AMP molecules bound in the cystathionine-beta-synthase domain.

The equilibrium between C2'- and C3'-endo conformations of nucleotides in solution, as well as their polymers DNA and RNA, has been well studied in previous work. However, this equilibrium of nucleotides in their binding state remains unclear. We observed two AMP molecules, in C3'- and C2'-endo conformations respectively, simultaneously bound to a cystathionine-beta-synthase (CBS) domain dimer of the magnesium and cobalt efflux protein CorC in the crystallographic study. The C2'-endo AMP molecule assumes the higher sugar pucker energy and one more hydrogen bond with the protein than the C3'-endo molecule does. The balance between the high sugar pucker energy and the low binding energy suggests an equilibrium or switch between C2'- and C3'-endo conformations of the bound nucleotides. Our work challenge the previous hypothesis that the ribose of the bound nucleotides would be locked in a fixed conformation.

A Potent In Vivo Antitumor Efficacy of Novel Recombinant Type I Interferon.

Purpose: Antiproliferative, antiviral, and immunomodulatory activities of endogenous type I IFNs (IFN1) prompt the design of recombinant IFN1 for therapeutic purposes. However, most of the designed IFNs exhibited suboptimal therapeutic efficacies against solid tumors. Here, we report evaluation of the in vitro and in vivo antitumorigenic activities of a novel recombinant IFN termed sIFN-I.Experimental Design: We compared primary and tertiary structures of sIFN-I with its parental human IFNα-2b, as well as affinities of these ligands for IFN1 receptor chains and pharmacokinetics. These IFN1 species were also compared for their ability to induce JAK-STAT signaling and expression of the IFN1-stimulated genes and to elicit antitumorigenic effects. Effects of sIFN-I on tumor angiogenesis and immune infiltration were also tested in transplanted and genetically engineered immunocompetent mouse models.Results: sIFN-I displayed greater affinity for IFNAR1 (over IFNAR2) chain of the IFN1 receptor and elicited a greater extent of IFN1 signaling and expression of IFN-inducible genes in human cells. Unlike IFNα-2b, sIFN-I induced JAK-STAT signaling in mouse cells and exhibited an extended half-life in mice. Treatment with sIFN-I inhibited intratumoral angiogenesis, increased CD8+ T-cell infiltration, and robustly suppressed growth of transplantable and genetically engineered tumors in immunodeficient and immunocompetent mice.Conclusions: These findings define sIFN-I as a novel recombinant IFN1 with potent preclinical antitumorigenic effects against solid tumor, thereby prompting the assessment of sIFN-I clinical efficacy in humans. Clin Cancer Res; 23(8); 2038-49. ©2016 AACR.

Pore-forming activity and structural autoinhibition of the gasdermin family.

Inflammatory caspases cleave the gasdermin D (GSDMD) protein to trigger pyroptosis, a lytic form of cell death that is crucial for immune defences and diseases. GSDMD contains a functionally important gasdermin-N domain that is shared in the gasdermin family. The functional mechanism of action of gasdermin proteins is unknown. Here we show that the gasdermin-N domains of the gasdermin proteins GSDMD, GSDMA3 and GSDMA can bind membrane lipids, phosphoinositides and cardiolipin, and exhibit membrane-disrupting cytotoxicity in mammalian cells and artificially transformed bacteria. Gasdermin-N moved to the plasma membrane during pyroptosis. Purified gasdermin-N efficiently lysed phosphoinositide/cardiolipin-containing liposomes and formed pores on membranes made of artificial or natural phospholipid mixtures. Most gasdermin pores had an inner diameter of 10­14 nm and contained 16 symmetric protomers. The crystal structure of GSDMA3 showed an autoinhibited two-domain architecture that is conserved in the gasdermin family. Structure-guided mutagenesis demonstrated that the liposome-leakage and pore-forming activities of the gasdermin-N domain are required for pyroptosis. These findings reveal the mechanism for pyroptosis and provide insights into the roles of the gasdermin family in necrosis, immunity and diseases.

Crystallographic observation of the movement of the membrane-distal domain of the T7SS core component EccB1 from Mycobacterium tuberculosis.

The protein EccB1, a core component of the type VII secretion system (T7SS) of Mycobacterium tuberculosis, has been identified as an ATPase and is essential for the secretion of virulence factors by the ESX-1 system. In a previous study, EccB1 structures were determined in two different conformations. Here, two new conformations are identified and described. These four conformations present snapshots of the swinging movement of the membrane-distal domain A2. The movement of this domain involves conformational changes in two flexible loops (loop A, residues 243-264, and loop B, residues 324-341) which are rich in proline and glycine residues and connect domain A2 to domains C1 and B2. It is proposed that the movement of this domain is related to the ATPase activity of EccB1 and its homologues, as well as to the substrate transport of ESX secretion systems.

Biochemical and structural characterization of a novel ubiquitin-conjugating enzyme E2 from Agrocybe aegeria reveals Ube2w family-specific properties.

Ubiquitination is a post-translational modification that is involved in myriad cellar regulation and disease pathways. The ubiquitin-conjugating enzyme (E2) is an important player in the ubiquitin transfer pathway. Although many E2 structures are available, not all E2 families have known structures, and three-dimensional structures from fungal organisms other than yeast are lacking. We report here the crystal structure of UbcA1, which is a novel ubiquitin-conjugating enzyme identified from the edible and medicinal mushroom Agrocybe aegerita and displays potential antitumor properties. The protein belongs to the Ube2w family and shows similar biochemical characteristics to human Ube2w, including monomer-dimer equilibrium in solution, α-NH2 ubiquitin-transfer activity and a mechanism to recognize backbone atoms of intrinsically disordered N-termini in substrates. Its structure displays a unique C-terminal conformation with an orientation of helix α3 that is completely different from the reported E2 structures but similar to a recently reported NMR ensemble of Ube2w. A mutagenesis study on this novel enzyme revealed that an intact C-terminus is significant for protein dimerization and enzymatic activity. As the first crystallized full-length protein of this family, UbcA1 may supersede the truncated X-ray structure of Ube2w (PDB entry 2A7L) as the representative structure of the Ube2w family.

Core component EccB1 of the Mycobacterium tuberculosis type VII secretion system is a periplasmic ATPase.

Pathogenic mycobacteria transport virulence factors across their complex cell wall via a type VII secretion system (T7SS)/early secreted antigenic target-6 of kDa secretion system (ESX). ESX conserved component (Ecc) B, a core component of the T7SS architecture, is predicted to be a membrane bound protein, but little is known about its structure and function. Here, we characterize EccB1, showing that it is an ATPase with no sequence or structural homology to other ATPases located in the cell envelope of Mycobacterium tuberculosis H37Rv. We obtained the crystal structure of an EccB1-ΔN72 truncated transmembrane helix and performed modeling and ATP docking studies, showing that EccB1 likely exists as a hexamer. Sequence alignment and ATPase activity determination of EccB1 homologues indicated the presence of 3 conserved motifs in the N- and C-terminals of EccB1-ΔN72 that assemble together between 2 membrane proximal domains of the EccB1-ΔN72 monomer. Models of the EccB1 hexamer show that 2 of the conserved motifs are involved in ATPase activity and form an ATP binding pocket located on the surface of 2 adjacent molecules. Our results suggest that EccB may act as the energy provider in the transport of T7SS virulence factors and may be involved in the formation of a channel across the mycomembrane.

Phillyrin attenuates LPS-induced pulmonary inflammation via suppression of MAPK and NF-κB activation in acute lung injury mice.

Phillyrin (Phil) is one of the main chemical constituents of Forsythia suspensa (Thunb.), which has shown to be an important traditional Chinese medicine. We tested the hypothesis that Phil modulates pulmonary inflammation in an ALI model induced by LPS. Male BALB/c mice were pretreated with or without Phil before respiratory administration with LPS, and pretreated with dexamethasone as a control. Cytokine release (TNF-α, IL-1ß, and IL-6) and amounts of inflammatory cell in bronchoalveolar lavage fluid (BALF) were detected by ELISA and cell counting separately. Pathologic changes, including neutrophil infiltration, interstitial edema, hemorrhage, hyaline membrane formation, necrosis, and congestion during acute lung injury in mice were evaluated via pathological section with HE staining. To further investigate the mechanism of Phil anti-inflammatory effects, activation of MAPK and NF-κB pathways was tested by western blot assay. Phil pretreatment significantly attenuated LPS-induced pulmonary histopathologic changes, alveolar hemorrhage, and neutrophil infiltration. The lung wet-to-dry weight ratios, as the index of pulmonary edema, were markedly decreased by Phil pretreatment. In addition, Phil decreased the production of the proinflammatory cytokines including (TNF-α, IL-1ß, and IL-6) and the concentration of myeloperoxidase (MPO) in lung tissues. Phil pretreatment also significantly suppressed LPS-induced activation of MAPK and NF-κB pathways in lung tissues. Taken together, the results suggest that Phil may have a protective effect on LPS-induced ALI, and it potentially contributes to the suppression of the activation of MAPK and NF-κB pathways. Phil may be a new preventive agent of ALI in the clinical setting.

Protective effect of esculentoside A on lipopolysaccharide-induced acute lung injury in mice.

BACKGROUND: Esculentoside A (EsA) is a saponin isolated from the Chinese herb Phytolacca esculenta. In our study, we sought to investigate the protective effects of EsA on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice. MATERIALS AND METHODS: To determine the effects of EsA on the reduction of histopathologic changes in mice with ALI, inflammatory cell count in bronchoalveolar lavage fluid (BALF) and lung wet-to-dry weight ratio were measured in LPS-challenged mice, and lung histopathologic changes observed via paraffin section were assessed. Next, cytokine production induced by LPS in BALF was measured by enzyme-linked immunosorbent assay. To further study the mechanism of EsA protective effects on ALI, IκBa, p38, and extracellular signal receptor-activated kinase pathways were investigated in lung tissue of mice with ALI. RESULTS: In the present investigation, EsA showed marked effects by reducing inflammatory infiltration, thickening of the alveolar wall, and pulmonary congestion. Levels of tumor necrosis factor α and interleukin 6 elevated by LPS were significantly decreased in BALF in EsA-pretreated ALI model. Furthermore, EsA significantly suppressed phosphorylation of IκBa, p38, and extracellular signal receptor-activated kinase. CONCLUSIONS: Taken together, our results suggest that EsA suppressed inflammatory responses in LPS-induced ALI through inhibition of the nuclear factor kappa B and mitogen activated protein kinase signaling pathways. EsA may be a promising potential preventive agent for ALI treatment.

Structural basis for the unique heterodimeric assembly between cerebral cavernous malformation 3 and germinal center kinase III.

Defects in cerebral cavernous malformation protein CCM3 result in cerebral cavernous malformation (CCM), a common vascular lesion of the human CNS. CCM3 functions as an adaptor protein that interacts with various signal proteins. Among these partner proteins, germinal center kinase III (GCKIII) proteins have attracted significant interest because GCKIII-CCM3 interactions play essential roles in vascular physiology. Here, we report the crystal structures of CCM3 in complex with the C-terminal regulatory domains of GCKIII (GCKIIIct) at 2.4 Å resolution. Our results reveal that GCKIIIct adopts a fold closely resembling that of the CCM3 N-terminal dimeric domain. GCKIIIct heterodimerizes with CCM3 in a manner analogous to CCM3 homodimerization. The remarkable structural rearrangement of CCM3 induced by GCKIIIct binding and the ensuing interactions within CCM3 are characterized as the structural determinants for GCKIIIct-CCM3 heterodimerization. Taken together, these findings provide a precise structural basis for GCKIIIct-CCM3 heterodimerization and the functional performance of GCKIII mediated by CCM3.

Sulfated derivatives of 20(S)-ginsenoside Rh2 and their inhibitory effects on LPS-induced inflammatory cytokines and mediators.

Ginsenoside Rh2 is one of the most important ginsenosides in ginseng with antitumor, antidiabetic, antiallergic, and anti-inflammatory effects. However, the extremely poor oral bioavailability induced by its low water solubility greatly limits the potency of Rh2 in clinical use. Therefore, in this study we sulfated 20(S)-ginsenoside Rh2 with chlorosulfonic acid and pyridine method, and got two new sulfated derivatives, Rh2-B1 and Rh2-B2, with higher water solubility. Their chemical structures were characterized by spectroscopic methods (IR, MS and NMR). Additionally, Rh2-B1 and Rh2-B2 had the greater anti-inflammatory effects than Rh2 through inhibiting inflammatory cytokines and mediators in LPS-induced mouse RAW264.7 macrophages cells. These results suggested that the sulfated modification of Rh2 improved its water solubility and the sulfated derivatives could be more potential candidates for developing as anti-inflammatory agents.

Crystal structure of TNF-α-inducing protein from Helicobacter pylori in active form reveals the intrinsic molecular flexibility for unique DNA-binding.

Tipα (TNF-α-inducing protein) from Helicobacter pylori is a carcinogenic effector. Studies on this protein revealed that a homodimer linked by a pair of intermolecular disulfide bridges (Cys25-Cys25 and Cys27-Cys27) was absolutely necessary for its biological functions. The activities of Tipα would be abolished when both disulfide bridges were disrupted. The crystal structures of Tipα reported to date, however, were based on inactive, monomeric mutants with their N-terminal, including residues Cys25 and Cys27, truncated. Here we report the crystal structure of H. pylori Tipα protein, TipαN(25), at 2.2Å resolution, in which Cys25 and Cys27 form a pair of inter-chain disulfide bridges linking an active dimer. The disulfide bridges exhibit structural flexibility in the present structure. A series of structure-based mutagenesis, biochemical assays and molecular dynamic simulations on DNA-Tipα interactions reveal that Tipα utilizes the dimeric interface as the DNA-binding site and that residues His60, Arg77 and Arg81 located at the interface are crucial for DNA binding. Tipα could bind to one ssDNA, two ssDNA or one dsDNA in experiments, respectively, in the native or mutant states. The unique DNA-binding activities of Tipα indicate that the intrinsic flexible nature of disulfide bridges could endow certain elasticity to the Tipα dimer for its unique bioactivities. The results shed light on the possible structural mechanism for the functional performances of Tipα.

Crystallization and preliminary crystallographic studies of CCM3 in complex with the C-terminal domain of MST4.

MST4 is a member of the GCKIII kinases. The interaction between cerebral cavernous malformation 3 (CCM3) and GCKIII kinases plays a critical role in cardiovascular development and in cerebral cavernous malformations. The complex of CCM3 and the C-terminal domain of MST4 has been constructed, purified and crystallized, and a diffraction data set has been collected to 2.4 Šresolution. The crystal of the CCM3-MST4 C-terminal domain complex belonged to space group P4(1)2(1)2 or P4(3)2(1)2, with unit-cell parameters a = 69.10, b = 69.10, c = 117.57 Å.

Crystal structures of aprataxin ortholog Hnt3 reveal the mechanism for reversal of 5'-adenylated DNA.

Aprataxin is a DNA deadenylase that resolves DNA 5'-AMP termini and reverses abortive DNA ligation. The crystal structures of Schizosaccharomyces pombe aprataxin Hnt3 in its apo form and in complex to dsDNA and dsDNA-AMP reveal how Hnt3 recognizes and processes 5'-adenylated DNA in a structure-specific manner. The bound DNA adopts a 5'-flap conformation that facilitates 5'-AMP access to the active site, where AMP cleavage occurs by a canonical catalytic mechanism.