Search

DNA strand breaks are repaired by DNA synthesis from an exposed DNA end paired with a homologous DNA template. DNA polymerase delta (Pol δ) catalyses DNA synthesis in multiple eukaryotic DNA break repair pathways but triggers genome instability unless its activity is restrained. We show that human HelQ halts DNA synthesis by isolated Pol δ and Pol δ-PCNA-RPA holoenzyme. Using novel HelQ mutant proteins we identify that inhibition of Pol δ is independent of DNA binding, and maps to a 70 amino acid intrinsically disordered region of HelQ. Pol δ and its POLD3 subunit robustly stimulated DNA single-strand annealing by HelQ, and POLD3 and HelQ interact physically via the intrinsically disordered HelQ region. This data, and inability of HelQ to inhibit DNA synthesis by the POLD1 catalytic subunit of Pol δ, reveal a mechanism for limiting DNA synthesis and promoting DNA strand annealing during human DNA break repair, which centres on POLD3.

Y-family DNA polymerase κ (Pol κ) can replicate damaged DNA templates to rescue stalled replication forks. Access of Pol κ to DNA damage sites is facilitated by its interaction with the processivity clamp PCNA and is regulated by PCNA mono-ubiquitylation. Here, we present cryo-EM reconstructions of human Pol κ bound to DNA, an incoming nucleotide, and wild type or mono-ubiquitylated PCNA (Ub-PCNA). In both reconstructions, the internal PIP-box adjacent to the Pol κ Polymerase-Associated Domain (PAD) docks the catalytic core to one PCNA protomer in an angled orientation, bending the DNA exiting the Pol κ active site through PCNA, while Pol κ C-terminal domain containing two Ubiquitin Binding Zinc Fingers (UBZs) is invisible, in agreement with disorder predictions. The ubiquitin moieties are partly flexible and extend radially away from PCNA, with the ubiquitin at the Pol κ-bound protomer appearing more rigid. Activity assays suggest that, when the internal PIP-box interaction is lost, Pol κ is retained on DNA by a secondary interaction between the UBZs and the ubiquitins flexibly conjugated to PCNA. Our data provide a structural basis for the recruitment of a Y-family TLS polymerase to sites of DNA damage., This research was supported by King Abdullah University of Science and Technology through core funding (to S.M.H.) and the Competitive Research Award Grant CRG8 URF/1/4036‐01‐01 (to S.M.H. and A.D.B.), and by the Wellcome Trust (to A.D.B.). R.C. acknowledges funding from the MINECO (CTQ2016-78636-P) and to AGAUR, (2017 SGR 324). The MD project has been carried out using CSUC resources. We acknowledge The Midlands Regional Cryo-EM Facility at the Leicester Institute of Structural and Chemical Biology (LISCB), major funding from MRC (MC_PC_17136). We thank Christos Savva (LISCB, University of Leicester) for his help in cryo-EM data collection and advice on data processing.

Nucleotide excision repair (NER) is critical for removing bulky DNA base lesions and avoiding diseases. NER couples lesion recognition by XPC to strand separation by XPB and XPD ATPases, followed by lesion excision by XPF and XPG nucleases. Here, we describe key regulatory mechanisms and roles of XPG for and beyond its cleavage activity. Strikingly, by combing single-molecule imaging and bulk cleavage assays, we found that XPG binding to the 7-subunit TFIIH core (coreTFIIH) stimulates coreTFIIH-dependent double-strand (ds)DNA unwinding 10-fold, and XPG-dependent DNA cleavage by up to 700-fold. Simultaneous monitoring of rates for coreTFIIH single-stranded (ss)DNA translocation and dsDNA unwinding showed XPG acts by switching ssDNA translocation to dsDNA unwinding as a likely committed step. Pertinent to the NER pathway regulation, XPG incision activity is suppressed during coreTFIIH translocation on DNA but is licensed when coreTFIIH stalls at the lesion or when ATP hydrolysis is blocked. Moreover, ≥15 nucleotides of 5'-ssDNA is a prerequisite for efficient translocation and incision. Our results unveil a paired coordination mechanism in which key lesion scanning and DNA incision steps are sequentially coordinated, and damaged patch removal is only licensed after generation of ≥15 nucleotides of 5'-ssDNA, ensuring the correct ssDNA bubble size before cleavage.Nucleotide excision repair (NER) removes bulky DNA lesions and is thereby crucial in maintaining transcription and genomic integrity. Here, the authors show a dual function for the XPG nuclease that is critical for finding and excising the damage. During the separation of the damage-containing strand from the undamaged strand, XPG stimulates TFIIH dependent dsDNA unwinding 10 fold. In return, when TFIIH stalls at the damage it stimulates XPG nuclease activity 700 fold. Remarkably, this mutually exclusive coordination requires a bubble longer than 15 nucleotides. This study addressees why a bubble of a certain size is needed to facilitate NER and why XPG is recruited at the beginning of NER when its endonucleolytic activity is required at the very end.

The activity of enzymes is traditionally characterised through bulk-phase biochemical methods that only report on population averages. Single-molecule methods are advantageous in elucidating kinetic and population heterogeneity but are often complicated, time consuming, and lack statistical power. We present a highly-generalisable and high-throughput single-molecule assay to rapidly characterise proteins involved in DNA metabolism. The assay exclusively relies on changes in total fluorescence intensity of surface-immobilised DNA templates as a result of DNA synthesis, unwinding or digestion. Combined with an automated data-analysis pipeline, our method provides enzymatic activity data of thousands of molecules in less than an hour. We demonstrate our method by characterising three fundamentally different enzyme activities: digestion by the phage λ exonuclease, synthesis by the phage Phi29 polymerase, and unwinding by the E. coli UvrD helicase. We observe the previously unknown activity of the UvrD helicase to remove neutravidin bound to 5′-, but not 3′-ends of biotinylated DNA.

DNA strand breaks can be repaired by base-pairing with unbroken homologous DNA, forming a template for new DNA synthesis that patches over the break site. In eukaryotes multiple DNA break repair pathways utilize DNA polymerase δ (Pol δ) to synthesise new DNA from the available 3’OH at the strand break. Here we show that DNA synthesis by human Pol δ is halted by the HelQ DNA repair protein directly targeting isolated Pol δ or Pol δ in complex with PCNA and RPA. The mechanism is independent of DNA binding by HelQ or Pol δ, maps to a region of HelQ that also modulates RPA, and requires multiple Pol δ subunits. Interaction of HelQ with the POLD3 subunit of Pol δ stimulated DNA single-strand annealing activity of HelQ. The data implicates HelQ in preventing genetic instability by restraining DNA synthesis in multiple DNA break repair pathways.

This work is based on our patent number “US 2015/0280017 A1”.; International audience; The process of effective solar energy harvesting and conversion requires efficient photon absorption, followed by charge generation and separation, then electron transfer. Nanostructured materials have been considered as potential building blocks for the development of future generations of solar cells. Much attention has been given to wide-bandgap semiconductor nanowires, combined and sensitized with low-bandgap semiconductors effectively attached to the nanowires for low-cost and highly efficient solar cells. Here, the in situ growth of lead sulfide (PbS) nanoparticles on the surface of zinc oxide (ZnO) nanowires grown by the Successive Ionic Layer Adsorption and Reaction (SILAR) technique is presented for different numbers of cycles. The morphology and structure of PbS nanoparticles are confirmed by Scanning Electron Microscopy (SEM), revealing the decoration of the nanowires with the PbS nanoparticles, Transmission Electron Microscopy (TEM) and HR-TEM, showing the tight attachment of PbS nanoparticles on the surface of the ZnO nanowires. The Selected Area Electron Diffraction (SAED) confirms the crystallization of the PbS. Photoluminescence spectra show a broad and more intense deep-level emission band.

Rapid, sensitive, and specific point-of-care testing for pathogens is crucial for disease control. Lateral flow assays (LFAs) have been employed for nucleic acid detection, but they have limited sensitivity and specificity. Here, we used a fusion of catalytically inactive SpCas9 endonuclease and VirD2 relaxase for sensitive, specific nucleic acid detection by LFA. In this assay, the target nucleic acid is amplified with biotinylated oligos. VirD2-dCas9 specifically binds the target sequence via dCas9 and covalently binds to a FAM-tagged oligonucleotide via VirD2. The biotin label and FAM tag are detected by a commercially available LFA. We coupled this system, named Vigilant (VirD2-dCas9 guided and LFA-coupled nucleic acid test), to reverse transcription-recombinase polymerase amplification to detect SARS-CoV2 in clinical samples. Vigilant exhibited a limit of detection of 2.5 copies/μL, comparable to CRISPR-based systems, and showed no cross-reactivity with SARS-CoV1 or MERS. Vigilant offers an easy-to-use, rapid, cost-effective, and robust detection platform for SARS-CoV2.

The activity of enzymes is traditionally characterised through bulk-phase biochemical methods that only report on population averages. Single-molecule methods are advantageous in elucidating kinetic and population heterogeneity but are often complicated, time consuming, and lacking statistical power. We present a highly generalisable and high-throughput single-molecule assay to rapidly characterise proteins involved in DNA metabolism. The assay exclusively relies on changes in total fluorescence intensity of surface-immobilised DNA templates as a result of DNA synthesis, unwinding or digestion. Combined with an automated data-analysis pipeline, our method provides enzymatic activity data of thousands of molecules in less than an hour. We demonstrate our method by characterising three fundamentally different nucleic-acid enzyme activities: digestion by the phage λ exonuclease, synthesis by the phage Phi29 polymerase, and unwinding by the E. coli UvrD helicase. We observe a previously unknown activity of the UvrD helicase to remove proteins tightly bound to the ends of DNA.

A large variety of fusion tags have been developed to improve protein expression, solubilization, and purification. Nevertheless, these tags have been combined in a rather limited number of composite tags and usually these composite tags have been dictated by traditional commercially‐available expression vectors. Moreover, most commercially‐available expression vectors include either N‐ or C‐terminal fusion tags but not both. Here, we introduce TSGIT, a fusion‐tag system composed of both N‐ and a C‐terminal composite fusion tags. The system includes two affinity tags, two solubilization tags and two cleavable tags distributed at both termini of the protein of interest. Therefore, the N‐ and the C‐terminal composite fusion tags in TSGIT are fully orthogonal in terms of both affinity selection and cleavage. For using TSGIT, we streamlined the cloning, expression, and purification procedures. Each component tag is selected to maximize its benefits toward the final construct. By expressing and partially purifying the protein of interest between the components of the TSGIT fusion, the full‐length protein is selected over truncated forms, which has been a long‐standing problem in protein purification. Moreover, due to the nature of the cleavable tags in TSGIT, the protein of interest is obtained in its native form without any additional undesired N‐ or C‐terminal amino acids. Finally, the resulting purified protein is ready for efficient ligation with other proteins or peptides for downstream applications. We demonstrate the use of this system by purifying a large amount of native fluorescent mRuby3 protein and bacteriophage T7 gp2.5 ssDNA‐binding protein.

The polyhistidine tag (His-tag) is one of the most popular protein tags used in the life sciences. Traditionally, the detection of His-tagged proteins relies on immunoblotting with anti-His antibodies. This approach is laborious for certain applications, such as protein purification, where time and simplicity are critical. The His-tag can also be directly detected by metal ion-loaded nickel-nitrilotriacetic acid-based chelator heads conjugated to fluorophores, which is a convenient alternative method to immunoblotting. Typically, such chelator heads are conjugated to either green or red fluorophores, the detection of which requires specialized excitation sources and detection systems. Here, we demonstrate that post-run staining is ideal for His-tag detection by metal ion-loaded and fluorescently labeled chelator heads in PAGE and blot membranes. Additionally, by comparing the performances of different chelator heads, we show how differences in microscopic affinity constants translate to macroscopic differences in the detection limits in environments with limited diffusion, such as PAGE. On the basis of these results, we devise a simple approach, called UVHis-PAGE, that uses metal ion-loaded and fluorescently labeled chelator heads to detect His-tagged proteins in PAGE and blot membranes. Our method uses a UV transilluminator as an excitation source, and the results can be visually inspected by the naked eye.

Selectins are key to mediating interactions involved in cellular adhesion and migration, underlying processes such as immune responses, metastasis, and transplantation. Selectins are composed of a lectin domain, an epidermal growth factor (EGF)-like domain, multiple short consensus repeats (SCRs), a transmembrane domain, and a cytoplasmic tail. It is well-established that the lectin and EGF domains are required to mediate interactions with ligands; however, the contributions of the other domains in mediating these interactions remain obscure. Using various E-selectin constructs produced in a newly developed silkworm-based expression system and several assays performed under both static and physiological flow conditions, including flow cytometry, glycan array analysis, surface plasmon resonance, and cell-rolling assays, we show here that a reduction in the number of SCR domains is correlated with a decline in functional E-selectin binding to hematopoietic cell E- and/or L-selectin ligand (HCELL) and P-selectin glycoprotein ligand-1 (PSGL-1). Moreover, the binding was significantly improved through E-selectin dimerization and by a substitution (A28H) that mimics an extended conformation of the lectin and EGF domains. Analyses of the association and dissociation rates indicated that the SCR domains, conformational extension, and dimerization collectively contribute to the association rate of E-selectin–ligand binding, whereas just the lectin and EGF domains contribute to the dissociation rate. These findings provide the first evidence of the critical role of the association rate in functional E-selectin–ligand interactions, and they highlight that the SCR domains have an important role that goes beyond the structural extension of the lectin and EGF domains.

In eukaryotes, DNA polymerase δ (Pol δ) bound to the proliferating cell nuclear antigen (PCNA) replicates the lagging strand and cooperates with flap endonuclease 1 (FEN1) to process the Okazaki fragments for their ligation. We present the high-resolution cryo-EM structure of the human processive Pol δ–DNA–PCNA complex in the absence and presence of FEN1. Pol δ is anchored to one of the three PCNA monomers through the C-terminal domain of the catalytic subunit. The catalytic core sits on top of PCNA in an open configuration while the regulatory subunits project laterally. This arrangement allows PCNA to thread and stabilize the DNA exiting the catalytic cleft and recruit FEN1 to one unoccupied monomer in a toolbelt fashion. Alternative holoenzyme conformations reveal important functional interactions that maintain PCNA orientation during synthesis. This work sheds light on the structural basis of Pol δ’s activity in replicating the human genome., Pol δ bound to the proliferating cell nuclear antigen (PCNA) replicates the lagging strand in eukaryotes and cooperates with flap endonuclease 1 (FEN1) to process the Okazaki fragments for their ligation. Here, the authors present a Cryo-EM structure of the human 4-subunit Pol δ bound to DNA and PCNA in a replicating state with an incoming nucleotide in the active site.

We developed a concurrent cyclic deracemisation approach for secondary alcohols that combines a non-stereospecific oxidation step and a stereoselective reduction step using two mutants of Thermoanaerobacter pseudoethanolicus secondary alcohol dehydrogenase (TeSADH) that exhibit various extents of stereoselectivities. In this approach, W110G TeSADH, a sparingly stereoselective mutant, performs the non-stereospecific oxidation step and W110V/G198D TeSADH performs the stereoselective reduction step. The use of orthogonal cofactor regeneration systems allowed for the spontaneous operation of these mutants. (S)-Configured alcohols were obtained in moderate ee's from their racemates using this strategy. To our knowledge, this report provides the first example of a fully enzymatic cyclic deracemisation with a stereoselective reduction step (CD-RS) for alcohols. This approach was further improved into a deracemisation strategy via stereoinversion using concurrent (R)-selective I86A TeSADH-catalysed oxidation that leaves (S)-alcohols untouched and W110V/G198D TeSADH-catalysed stereoselective reduction of the resultant ketone intermediates into the corresponding (S)-configured alcohols. The latter strategy enabled quantitative production of (S)-1-phenylethanol in >99% ee from its racemate. Overall, we show the superiority of the stereoinversion deracemisation approach for alcohols when compared with cyclic deracemisation, which is mainly due to the elimination of futile cycles in the former.

Precise genome editing by systems such as clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) requires high-efficiency homology-directed repair (HDR). Different technologies have been developed to improve HDR but with limited success. Here, we generated a fusion between the Cas9 endonuclease and the Agrobacterium VirD2 relaxase (Cas9-VirD2). This chimeric protein combines the functions of Cas9, which produces targeted and specific DNA double-strand breaks (DSBs), and the VirD2 relaxase, which brings the repair template in close proximity to the DSBs, to facilitate HDR. We successfully employed our Cas9-VirD2 system for precise ACETOLACTATE SYNTHASE (OsALS) allele modification to generate herbicide-resistant rice (Oryza sativa) plants, CAROTENOID CLEAVAGE DIOXYGENASE-7 (OsCCD7) to engineer plant architecture, and generate in-frame fusions with the HA epitope at HISTONE DEACETYLASE (OsHDT) locus. The Cas9-VirD2 system expands our ability to improve agriculturally important traits in crops and opens new possibilities for precision genome engineering across diverse eukaryotic species., Ali, Shami, Sedeek et al. generate a fusion between Cas9 and the VirD2 relaxase (Cas9-VirD2), which combines the functions of both proteins in producing targeted and specific double strand breaks and promoting homology-directed repair. They show the utility of their method by producing herbicide resistant rice.

Dicer-like 1 (DCL1) is a core component of the plant microRNA (miRNA) biogenesis machinery. MiRNA is transcribed as a precursor RNA, termed primary miRNA (pri-miRNA), which is cleaved by DCL1 in two steps to generate miRNA/miRNA* duplex. Pri-miRNA is a single-stranded RNA that forms a hairpin structure with a number of unpaired bases, hereafter called mismatches, on its stem. In the present study, by using purified recombinant Arabidopsis DCL1, we presented evidence that mismatches on the stem of pri-miRNA are important for precise DCL1 cleavage. We showed that a mismatch at the loop-distal side of the end of miRNA/miRNA* duplex is important for efficient cleavage of pri-miRNA in vitro, as previously suggested in planta. On the contrary, mismatches distant from the miRNA/miRNA* duplex region are important for determining the cleavage position by DCL1. The purified DCL1 proteins cleaved mutant pri-miRNA variants without such mismatches at a position at which wild-type pri-miRNA variants are not usually cleaved, resulting in an increased accumulation of small RNA different from miRNA. Therefore, our results suggest that, in addition to the distance from the ssRNA-dsRNA junction, mismatches on the stem of pri-miRNA function as a determinant for precise processing of pri-miRNA by DCL1 in plants.

Protein purification by affinity chromatography relies primarily on the interaction of a fused-tag to the protein of interest. Here, we describe a tag-free affinity method that employs functional selection interactions to a broad range of proteins. To achieve this, we coupled human DNA-clamp proliferating cell nuclear antigen (PCNA) that interacts with over one hundred proteins to an agarose resin. We demonstrate the versatility of our PCNA-Agarose column at various chromatographic steps by purifying PCNA-binding proteins that are involved in DNA Replication (DNA polymerase δ, flap endonuclease 1 and DNA ligase 1), translesion DNA synthesis (DNA polymerases eta, kappa and iota) and genome stability (p15). We also show the competence of the PCNA-Agarose column to purify non-PCNA binding proteins by fusing the PCNA-binding motif of human p21 as an affinity tag. Finally, we establish that our PCNA-Agarose column is a suitable analytical method for characterizing the binding strength of PCNA-binding proteins. The conservation and homology of PCNA-like clamps will allow for the immediate extension of our method to other species.

Molecular diagnosis and surveillance of pathogens such as SARS‐CoV‐2 depend on nucleic acid isolation. Pandemics at the scale of COVID‐19 can cause a global shortage of proprietary commercial reagents and BSL‐2 laboratories to safely perform testing. Therefore, alternative solutions are urgently needed to address these challenges. An open‐source method, magnetic‐nanoparticle‐aided viral RNA isolation from contagious samples (MAVRICS), built upon readily available reagents, and easily assembled in any basically equipped laboratory, is thus developed. The performance of MAVRICS is evaluated using validated pathogen detection assays and real‐world and contrived samples. Unlike conventional methods, MAVRICS works directly in samples inactivated in phenol‐chloroform (e.g., TRIzol), thus allowing infectious samples to be handled safely without biocontainment facilities. MAVRICS allows wastewater biomass immobilized on membranes to be directly inactivated and lysed in TRIzol followed by RNA extraction by magnetic nanoparticles, thereby greatly reducing biohazard risk and simplifying processing procedures. Using 39 COVID‐19 patient samples and two wastewater samples, it is shown that MAVRICS rivals commercial kits in detection of SARS‐CoV‐2, influenza viruses, and respiratory syncytial virus. Therefore, MAVRICS is safe, fast, and scalable. It is field‐deployable with minimal equipment requirements and could become an enabling technology for widespread testing and wastewater monitoring of diverse pathogens., One important bottleneck in the diagnosis and surveillance of COVID‐19 is the shortage of kits for RNA extraction. Magnetic‐nanoparticle‐aided viral RNA isolation from contagious samples (MAVRICS) is an open‐source, safe, fast, and scalable method for RNA extraction. MAVRICS rivals commercial kits but requires minimal materials, and thus could become an enabling technology for widespread community testing of diverse pathogens.

Critical for transcription initiation and bulky lesion DNA repair, TFIIH provides an exemplary system to connect molecular mechanisms to biological outcomes due to its strong genetic links to different specific human diseases. Recent advances in structural and computational biology provide a unique opportunity to re-examine biologically relevant molecular structures and develop possible mechanistic insights for the large dynamic TFIIH complex. TFIIH presents many puzzles involving how its two SF2 helicase family enzymes, XPB and XPD, function in transcription initiation and repair: how do they initiate transcription, detect and verify DNA damage, select the damaged strand for incision, coordinate repair with transcription and cell cycle through Cdk-activating-kinase (CAK) signaling, and result in very different specific human diseases associated with cancer, aging, and development from single missense mutations? By joining analyses of breakthrough cryo-electron microscopy (cryo-EM) structures and advanced computation with data from biochemistry and human genetics, we develop unified concepts and molecular level understanding for TFIIH functions with a focus on structural mechanisms. We provocatively consider that TFIIH may have first evolved from evolutionary pressure for TCR to resolve arrested transcription blocks to DNA replication and later added its key roles in transcription initiation and global DNA repair. We anticipate that this level of mechanistic information will have significant impact on thinking about TFIIH, laying a robust foundation suitable to develop new paradigms for DNA transcription initiation and repair along with insights into disease prevention, susceptibility, diagnosis and interventions.

Highlights • RT-LAMP coupled with CRISPR-Cas12 provides a sensitive and specific virus detection platform. • iSCAN sensitivity and specificity are comparable with RT-qPCR. • iSCAN is a 1 h detection module that can help in testing in low resource areas. • iSCAN can be developed as a one-pot assay. • iSCAN reagents can be produced locally and deployed for SARS-CoV2 detection., The COVID-19 pandemic caused by SARS-CoV-2 affects all aspects of human life. Detection platforms that are efficient, rapid, accurate, specific, sensitive, and user friendly are urgently needed to manage and control the spread of SARS-CoV-2. RT-qPCR based methods are the gold standard for SARS-CoV-2 detection. However, these methods require trained personnel, sophisticated infrastructure, and a long turnaround time, thereby limiting their usefulness. Reverse transcription-loop-mediated isothermal amplification (RT-LAMP), a one-step nucleic acid amplification method conducted at a single temperature, has been used for colorimetric virus detection. CRISPR-Cas12 and CRISPR-Cas13 systems, which possess collateral activity against ssDNA and RNA, respectively, have also been harnessed for virus detection. Here, we built an efficient, rapid, specific, sensitive, user-friendly SARS-CoV-2 detection module that combines the robust virus amplification of RT-LAMP with the specific detection ability of SARS-CoV-2 by CRISPR-Cas12. Furthermore, we combined the RT-LAMP-CRISPR-Cas12 module with lateral flow cells to enable highly efficient point-of-care SARS-CoV-2 detection. Our iSCAN SARS-CoV-2 detection module, which exhibits the critical features of a robust molecular diagnostic device, should facilitate the effective management and control of COVID-19.

One-step RT-qPCR is the most widely applied method for COVID-19 diagnostics. Designing in-house one-step RT-qPCR kits is restricted by the patent-rights for the production of enzymes and the lack of information about the components of the commercial kits. Here, we provide a simple, economical, and powerful one-step RT-qPCR kit based on patent-free, specifically-tailored versions of Moloney Murine Leukemia Virus Reverse Transcriptase and Thermus aquaticus DNA polymerase termed the R3T (Rapid Research Response Team) One-step RT-qPCR. Our kit was routinely able to reliably detect as low as 10 copies of the synthetic RNAs of the SARS-CoV-2. More importantly, our kit successfully detected COVID-19 in clinical samples of broad viral titers with similar reliability and selectivity as that of the Invitrogen SuperScript™ III Platinum™ One-step RT-qPCR and TaqPath™ 1-Step RT-qPCR kits. Overall, our kit has shown robust performance in both of laboratory settings and the Saudi Ministry of Health-approved testing facility.

Replacement of the stalled replicative polymerase (Pol δ) at a DNA lesion by the error-prone DNA polymerase κ (Pol κ) restarts synthesis past the lesion to prevent genome instability. The switching from Pol δ to Pol κ is mediated by the processivity clamp PCNA but the structural basis of this mechanism is unknown. We determined the Cryo-EM structures of human Pol κ–DNA–PCNA complex and of a stalled Pol δ–DNA–PCNA complex at 3.9 and 4.7 Å resolution, respectively. In Pol κ complex, the C-terminus of the PAD domain docks the catalytic core to one PCNA protomer in an angled orientation, bending the DNA exiting Pol κ active site through PCNA. In Pol δ complex, the DNA is disengaged from the active site but is retained by the thumb domain. We present a model for polymerase switching facilitated by Pol κ recruitment to PCNA and Pol κ conformational sampling to seize the DNA from stalled Pol δ assisted by PCNA tilting.

Diagnosis and surveillance of emerging pathogens such as SARS-CoV-2 depend on nucleic acid isolation from clinical and environmental samples. Under normal circumstances, samples would be processed using commercial proprietary reagents in Biosafety 2 (BSL-2) or higher facilities. A pandemic at the scale of COVID-19 has caused a global shortage of proprietary reagents and BSL-2 laboratories to safely perform testing. Therefore, alternative solutions are urgently needed to address these challenges. We developed an open-source method calledMagnetic-nanoparticle-AidedViralRNAIsolation ofContagiousSamples (MAVRICS) that is built upon reagents that are either readily available or can be synthesized in any molecular biology laboratory with basic equipment. Unlike conventional methods, MAVRICS works directly in samples inactivated in acid guanidinium thiocyanate-phenol-chloroform (e.g., TRIzol), thus allowing infectious samples to be handled safely without biocontainment facilities. Using 36 COVID-19 patient samples, 2 wastewater samples and 1 human pathogens control sample, we showed that MAVRICS rivals commercial kits in validated diagnostic tests of SARS-CoV-2, influenza viruses, and respiratory syncytial virus. MAVRICS is scalable and thus could become an enabling technology for widespread community testing and wastewater monitoring in the current and future pandemics.

The COVID-19 pandemic caused by SARS-CoV-2 affects all aspects of human life. Detection platforms that are efficient, rapid, accurate, specific, sensitive, and user friendly are urgently needed to manage and control the spread of SARS-CoV-2. RT-qPCR based methods are the gold standard for SARS-CoV-2 detection. However, these methods require trained personnel, sophisticated infrastructure, and a long turnaround time, thereby limiting their usefulness. Reverse transcription-loop-mediated isothermal amplification (RT-LAMP), a one-step nucleic acid amplification method conducted at a single temperature, has been used for colorimetric virus detection. CRISPR-Cas12 and CRISPR-Cas13 systems, which possess collateral activity against ssDNA and RNA, respectively, have also been harnessed for virus detection. Here, we built an efficient, rapid, specific, sensitive, user-friendly SARS-CoV-2 detection module that combines the robust virus amplification of RT-LAMP with the specific detection ability of SARS-CoV-2 by CRISPR-Cas12. Furthermore, we combined the RT-LAMP-CRISPR-Cas12 module with lateral flow cells to enable highly efficient point-of-care SARS-CoV-2 detection. Our iSCAN SARS-CoV-2 detection module, which exhibits the critical features of a robust molecular diagnostic device, should facilitate the effective management and control of COVID-19.

The authors acknowledge the support provided by the Deanship of Scientific Research (DSR) at King Fahd University of Petroleum and Minerals (KFUPM) for funding this work under project number IN151032. They also acknowledge the supported by baseline research fund to S.M.H. by King Abdullah University of Science and Technology.

The deep-sea brines of the Red Sea are remote and unexplored environments characterized by high temperatures, anoxic water, and elevated concentrations of salt and heavy metals. This environment provides a rare system to study the interplay between halophilic and thermophilic adaptation in biologic macromolecules. The present article reports the first DNA polymerase with halophilic and thermophilic features. Biochemical and structural analysis by Raman and circular dichroism spectroscopy showed that the charge distribution on the protein's surface mediates the structural balance between stability for thermal adaptation and flexibility for counteracting the salt-induced rigid and nonfunctional hydrophobic packing. Salt bridge interactions via increased negative and positive charges contribute to structural stability. Salt tolerance, conversely, is mediated by a dynamic structure that becomes more fixed and functional with increasing salt concentration. We propose that repulsive forces among excess negative charges, in addition to a high percentage of negatively charged random coils, mediate this structural dynamism. This knowledge enabled us to engineer a halophilic version of Thermococcus kodakarensis DNA polymerase.-Takahashi, M., Takahashi, E., Joudeh, L. I., Marini, M., Das, G., Elshenawy, M. M., Akal, A., Sakashita, K., Alam, I., Tehseen, M., Sobhy, M. A., Stingl, U., Merzaban, J. S., Di Fabrizio, E., Hamdan, S. M. Dynamic structure mediates halophilic adaptation of a DNA polymerase from the deep-sea brines of the Red Sea.

The KOD DNA polymerase from Thermococcus kodakarensis (Tkod-Pol) has been preferred for PCR due to its rapid elongation rate, extreme thermostability and outstanding fidelity. Here in this study, we utilized silkworm-baculovirus expression vector system (silkworm-BEVS) to express the recombinant Tkod-Pol (rKOD) with N-terminal (rKOD-N) or C-terminal (rKOD-C) tandem fusion tags. By using BEVS, we produced functional rKODs with satisfactory yields, about 1.1 mg/larva for rKOD-N and 0.25 mg/larva for rKOD-C, respectively. Interestingly, we found that rKOD-C shows higher thermostability at 95 °C than that of rKOD-N, while that rKOD-N is significantly unstable after exposing to long period of heat-shock. We also assessed the polymerase activity as well as the fidelity of purified rKODs under various conditions. Compared with commercially available rKOD, which is expressed in E. coli expression system, rKOD-C exhibited almost the same PCR performance as the commercial rKOD did, while rKOD-N did lower performance. Taken together, our results suggested that silkworm-BEVS can be used to express and purify efficient rKOD in a commercial way.

Here, ketones bearing two bulky substituents, named bulky-bulky ketones, were successfully reduced to their corresponding optically-enriched alcohols using various mutants of Thermoanaerobacter pseudoethanolicus secondary alcohol dehydrogenase (TeSADH). Substituted 2-tetralones in particular were reduced to 2-tetralols with high conversion and high enantioselectivity. The pharmacological importance of substituted 2-tetralols as key drug-building blocks makes our biocatalytic reduction method a highly essential tool. We showed that changing the position of the substituent on the aromatic ring of 2-tetralones impacted their binding affinity and the reaction maximum catalytic rate. Docking studies with several TeSADH mutants explained how the position of the substituent on the tetralone influences the binding orientation of substituted 2-tetralones and their reaction stereoselectivity.

The strength of the biotin/avidin interaction makes it an ideal tool for the purification of biotin-labeled proteins via avidin-coupled resin with high specificity and selectivity. Nevertheless, this tight binding comes at an extra cost of performing the elution step under denaturing conditions. Weakening the biotin/avidin interaction improves the elution conditions, but only to mild or harsh denaturing buffers with the drawback of reducing the specificity and selectivity of this interaction. Here, we present two chromatographic protein purification schemes that are well-suited for application under native conditions thus preserving the strength of the biotin/avidin interaction. In the first scheme, we introduce a biotin-labeled SUMO-tag to each of human flap endonuclease 1 and Escherichia coli replication termination protein Tus, and elute both proteins by performing on-resin cleavage using SUMO protease. In the second scheme, we immobilize biotin-labeled human proliferating cell nuclear antigen (PCNA) on the avidin-coupled resin and use the resulting resin as a tag-free affinity method to purify the PCNA-binding protein human DNA Ligase 1. Furthermore, we streamlined the protein biotinylation protocol by constructing a single plasmid expression system that ensures high level of expression and solubility for each of the target protein bearing the biotin-tag and the enzyme responsible for the in vivo biotinylation reaction. Both chromatographic schemes resulted in a high yield of pure proteins in their native form.

Bulk methods measure the ensemble behavior of molecules, in which individual reaction rates of the underlying steps are averaged throughout the population. Single-molecule Förster resonance energy transfer (smFRET) provides a recording of the conformational changes taking place by individual molecules in real-time. Therefore, smFRET is powerful in measuring structural changes in the enzyme or substrate during binding and catalysis. This work presents a protocol for single-molecule imaging of the interaction of a four-way Holliday junction (HJ) and gap endonuclease I (GEN1), a cytosolic homologous recombination enzyme. Also presented are single-color and two-color alternating excitation (ALEX) smFRET experimental protocols to follow the resolution of the HJ by GEN1 in real-time. The kinetics of GEN1 dimerization are determined at the HJ, which has been suggested to play a key role in the resolution of the HJ and has remained elusive until now. The techniques described here can be widely applied to obtain valuable mechanistic insights of many enzyme-DNA systems.

Protein-induced fluorescence enhancement (PIFE) is a popular tool for characterizing protein-DNA interactions. PIFE has been explained by an increase in local viscosity due to the presence of the protein residues. This explanation, however, denies the opposite effect of fluorescence quenching. This work offers a perspective for understanding PIFE mechanism and reports the observation of a phenomenon that we name protein-induced fluorescence quenching (PIFQ), which exhibits an opposite effect to PIFE. A detailed characterization of these two fluorescence modulations reveals that the initial fluorescence state of the labeled mediator (DNA) determines whether this mediator-conjugated dye undergoes PIFE or PIFQ upon protein binding. This key role of the mediator DNA provides a protocol for the experimental design to obtain either PIFQ or PIFE, on-demand. This makes the arbitrary nature of the current experimental design obsolete, allowing for proper integration of both PIFE and PIFQ with existing bulk and single-molecule fluorescence techniques., Protein-induced fluorescence enhancement (PIFE) is a popular tool for characterizing protein-DNA interactions. Here, authors provide a perspective on understanding the general phenomenon of induced fluorescence modulation

Human GEN1 is a cytosolic homologous recombination protein that resolves persisting four-way Holliday junctions (HJ) after the dissolution of the nuclear membrane. GEN1 dimerization has been suggested to play key role in the resolution of the HJ, but the kinetic details of its reaction remained elusive. Here, single-molecule FRET shows how human GEN1 binds the HJ and always ensures its resolution within the lifetime of the GEN1-HJ complex. GEN1 monomer generally follows the isomer bias of the HJ in its initial binding and subsequently distorts it for catalysis. GEN1 monomer remains tightly bound with no apparent dissociation until GEN1 dimer is formed and the HJ is fully resolved. Fast on- and slow off-rates of GEN1 dimer and its increased affinity to the singly-cleaved HJ enforce the forward reaction. Furthermore, GEN1 monomer binds singly-cleaved HJ tighter than intact HJ providing a fail-safe mechanism if GEN1 dimer or one of its monomers dissociates after the first cleavage. The tight binding of GEN1 monomer to intact- and singly-cleaved HJ empowers it as the last resort to process HJs that escape the primary mechanisms.

A critical bottleneck in COVID‐19 diagnosis and surveillance is the shortage of kits for RNA extraction. In article number 2000068, Mo Li and co‐workers develop a DIY, open‐source, safe, and fast method for magnetic‐nanoparticle‐aided viral RNA isolation from contagious samples (MAVRICS). MAVRICS rivals commercial kits in performance and could become an enabling technology for community testing and wastewater monitoring in the current and future pandemics.