Functional Selection of Tau Oligomerization-Inhibiting Aptamers.

Pathological hyperphosphorylation and aggregation of microtubule-associated Tau protein contribute to Alzheimer's Disease (AD) and other related tauopathies. Currently, no cure exists for Alzheimer's Disease. Aptamers offer significant potential as next-generation therapeutics in biotechnology and the treatment of neurological disorders. Traditional aptamer selection methods for Tau protein focus on binding affinity rather than interference with pathological Tau. In this study, we developed a new selection strategy to enrich DNA aptamers that bind to surviving monomeric Tau protein under conditions that would typically promote Tau aggregation. Employing this approach, we identified a set of aptamer candidates. Notably, BW1c demonstrates a high binding affinity (Kd=6.6 nM) to Tau protein and effectively inhibits arachidonic acid (AA)-induced Tau protein oligomerization and aggregation. Additionally, it inhibits GSK3ß-mediated Tau hyperphosphorylation in cell-free systems and okadaic acid-mediated Tau hyperphosphorylation in cellular milieu. Lastly, retro-orbital injection of BW1c tau aptamer shows the ability to cross the blood brain barrier and gain access to neuronal cell body. Through further refinement and development, these Tau aptamers may pave the way for a first-in-class neurotherapeutic to mitigate tauopathy-associated neurodegenerative disorders.

Ligand-Guided Selection with Artificially Expanded Genetic Information Systems against TCR-CD3ε.

Here we are reporting, for the first time, a ligand-guided selection (LIGS) experiment using an artificially expanded genetic information system (AEGIS) to successfully identify an AEGIS-DNA aptamer against T cell receptor-CD3ε expressed on Jurkat.E6 cells. Thus, we have effectively combined the enhanced diversity of an AEGIS DNA library with LIGS to develop a superior screening platform to discover superior aptamers. Libraries of DNA molecules from highly diversified building blocks will provide better ligands due to more functional diversity and better-controlled folding. Thus, a DNA library with AEGIS components (dZ and dP) was used in LIGS experiments against TCR-CD3ε in its native state using two clinically relevant monoclonal antibodies to identify an aptamer termed JZPO-10, with nanomolar affinity. Multiple specificity assays using knockout cells, and competition experiments using monoclonal antibodies utilized in LIGS, show unprecedented specificity of JZPO-10, suggesting that the combination of LIGS with AEGIS-DNA libraries will provide a superior screening platform to discover artificial ligands against critical cellular targets.

Nucleoside analogs to manage sequence divergence in nucleic acid amplification and SNP detection.

Described here are the synthesis, enzymology and some applications of a purine nucleoside analog (H) designed to have two tautomeric forms, one complementary to thymidine (T), the other complementary to cytidine (C). The performance of H is compared by various metrics to performances of other 'biversal' analogs that similarly rely on tautomerism to complement both pyrimidines. These include (i) the thermodynamic stability of duplexes that pair these biversals with various standard nucleotides, (ii) the ability of the biversals to support polymerase chain reaction (PCR), (iii) the ability of primers containing biversals to equally amplify targets having polymorphisms in the primer binding site, and (iv) the ability of ligation-based assays to exploit the biversals to detect medically relevant single nucleotide polymorphisms (SNPs) in sequences flanked by medically irrelevant polymorphisms. One advantage of H over the widely used inosine 'universal base' and 'mixed sequence' probes is seen in ligation-based assays to detect SNPs. The need to detect medically relevant SNPs within ambiguous sequences is especially important when probing RNA viruses, which rapidly mutate to create drug resistance, but also suffer neutral drift, the second obstructing simple methods to detect the first. Thus, H is being developed to detect variants of viruses that are rapidly mutating.

An Aptamer-Nanotrain Assembled from Six-Letter DNA Delivers Doxorubicin Selectively to Liver Cancer Cells.

Expanding the number of nucleotides in DNA increases the information density of functional DNA molecules, creating nanoassemblies that cannot be invaded by natural DNA/RNA in complex biological systems. Here, we show how six-letter GACTZP DNA contributes this property in two parts of a nanoassembly: 1) in an aptamer evolved from a six-letter DNA library to selectively bind liver cancer cells; and 2) in a six-letter self-assembling GACTZP nanotrain that carries the drug doxorubicin. The aptamer-nanotrain assembly, charged with doxorubicin, selectively kills liver cancer cells in culture, as the selectivity of the aptamer binding directs doxorubicin into the aptamer-targeted cells. The assembly does not kill untransformed cells that the aptamer does not bind. This architecture, built with an expanded genetic alphabet, is reminiscent of antibodies conjugated to drugs, which presumably act by this mechanism as well, but with the antibody replaced by an aptamer.

Point of sampling detection of Zika virus within a multiplexed kit capable of detecting dengue and chikungunya.

BACKGROUND: Zika, dengue, and chikungunya are three mosquito-borne viruses having overlapping transmission vectors. They cause diseases having similar symptoms in human patients, but requiring different immediate management steps. Therefore, rapid (< one hour) discrimination of these three viruses in patient samples and trapped mosquitoes is needed. The need for speed precludes any assay that requires complex up-front sample preparation, such as extraction of nucleic acids from the sample. Also precluded in robust point-of-sampling assays is downstream release of the amplicon mixture, as this risks contamination of future samples that will give false positives. METHODS: Procedures are reported that directly test urine and plasma (for patient diagnostics) or crushed mosquito carcasses (for environmental surveillance). Carcasses are captured on paper samples carrying quaternary ammonium groups (Q-paper), which may be directly introduced into the assay. To avoid the time and instrumentation requirements of PCR, the procedure uses loop-mediated isothermal amplification (LAMP). Downstream detection is done in sealed tubes, with dTTP-dUTP mixtures in the LAMP with a thermolabile uracil DNA glycosylase (UDG); this offers a second mechanism to prevent forward contamination. Reverse transcription LAMP (RT-LAMP) reagents are distributed dry without requiring a continuous chain of refrigeration. RESULTS: The tests detect viral RNA in unprocessed urine and other biological samples, distinguishing Zika, chikungunya, and dengue in urine and in mosquitoes infected with live Zika and chikungunya viruses. The limits of detection (LODs) are ~0.71 pfu equivalent viral RNAs for Zika, ~1.22 pfu equivalent viral RNAs for dengue, and ~38 copies of chikungunya viral RNA. A handheld, battery-powered device with an orange filter was constructed to visualize the output. Preliminary data showed that this architecture, working with pre-prepared tubes holding lyophilized reagent/enzyme mixtures and shipped without a chain of refrigeration, also worked with human plasma samples to detect chikungunya and dengue in Pune, India. CONCLUSIONS: A kit, complete with a visualization device, is now available for point-of-sampling detection of Zika, chikungunya, and dengue. The assay output is read in ca. 30 min by visualizing (human eye) three-color coded fluorescence signals. Assay in dried format allows it to be run in low-resource environments.

In vitro selection with artificial expanded genetic information systems.

Artificially expanded genetic information systems (AEGISs) are unnatural forms of DNA that increase the number of independently replicating nucleotide building blocks. To do this, AEGIS pairs are joined by different arrangements of hydrogen bond donor and acceptor groups, all while retaining their Watson-Crick geometries. We report here a unique case where AEGIS DNA has been used to execute a systematic evolution of ligands by exponential enrichment (SELEX) experiment. This AEGIS-SELEX was designed to create AEGIS oligonucleotides that bind to a line of breast cancer cells. AEGIS-SELEX delivered an AEGIS aptamer (ZAP-2012) built from six different kinds of nucleotides (the standard G, A, C, and T, and the AEGIS nonstandard P and Z nucleotides, the last having a nitro functionality not found in standard DNA). ZAP-2012 has a dissociation constant of 30 nM against these cells. The affinity is diminished or lost when Z or P (or both) is replaced by standard nucleotides and compares well with affinities of standard GACT aptamers selected against cell lines using standard SELEX. The success of AEGIS-SELEX relies on various innovations, including (i) the ability to synthesize GACTZP libraries, (ii) polymerases that PCR amplify GACTZP DNA with little loss of the AEGIS nonstandard nucleotides, and (iii) technologies to deep sequence GACTZP DNA survivors. These results take the next step toward expanding the power and utility of SELEX and offer an AEGIS-SELEX that could possibly generate receptors, ligands, and catalysts having sequence diversities nearer to that displayed by proteins.

Aptamers against Cells Overexpressing Glypican†3 from Expanded Genetic Systems Combined with Cell Engineering and Laboratory Evolution.

Laboratory in vitro evolution (LIVE) might deliver DNA aptamers that bind proteins expressed on the surface of cells. In this work, we used cell engineering to place glypican 3 (GPC3), a possible marker for liver cancer theranostics, on the surface of a liver cell line. Libraries were then built from a six-letter genetic alphabet containing the standard nucleobases and two added nucleobases (2-amino-8H-imidazo[1,2-a][1,3,5]triazin-4-one and 6-amino-5-nitropyridin-2-one), Watson-Crick complements from an artificially expanded genetic information system (AEGIS). With counterselection against non-engineered cells, eight AEGIS-containing aptamers were recovered. Five bound selectively to GPC3-overexpressing cells. This selection-counterselection scheme had acceptable statistics, notwithstanding the possibility that cells engineered to overexpress GPC3 might also express different off-target proteins. This is the first example of such a combination.

Evolution of functional six-nucleotide DNA.

Axiomatically, the density of information stored in DNA, with just four nucleotides (GACT), is higher than in a binary code, but less than it might be if synthetic biologists succeed in adding independently replicating nucleotides to genetic systems. Such addition could also add functional groups not found in natural DNA, but useful for molecular performance. Here, we consider two new nucleotides (Z and P, 6-amino-5-nitro-3-(1'-ß-D-2'-deoxyribo-furanosyl)-2(1H)-pyridone and 2-amino-8-(1'-ß-D-2'-deoxyribofuranosyl)-imidazo[1,2-a]-1,3,5-triazin-4(8H)-one). These are designed to pair via complete Watson-Crick geometry. These were added to a library of oligonucleotides used in a laboratory in vitro evolution (LIVE) experiment; the GACTZP library was challenged to deliver molecules that bind selectively to liver cancer cells, but not to untransformed liver cells. Unlike in classical in vitro selection, low levels of mutation allow this system to evolve to create binding molecules not necessarily present in the original library. Over a dozen binding species were recovered. The best had Z and/or P in their sequences. Several had multiple, nearby, and adjacent Zs and Ps. Only the weaker binders contained no Z or P at all. This suggests that this system explored much of the sequence space available to this genetic system and that GACTZP libraries are richer reservoirs of functionality than standard libraries.

Helicase-Dependent Isothermal Amplification of DNA and RNA by Using Self-Avoiding Molecular Recognition Systems.

Assays that detect DNA or RNA (xNA) are highly sensitive, as small amounts of xNA can be amplified by PCR. Unfortunately, PCR is inconvenient in low-resource environments, and requires equipment and power that might not be available in these environments. Isothermal procedures, which avoid thermal cycling, are often confounded by primer dimers, off-target priming, and other artifacts. Here, we show how a "self avoiding molecular recognition system" (SAMRS) eliminates these artifacts and gives clean amplicons in a helicase-dependent isothermal amplification (SAMRS-HDA). We also show that incorporating SAMRS into the 3'-ends of primers facilitates the design and screening of primers for HDA assays. Finally, we show that SAMRS-HDA can be twofold multiplexed, difficult to achieve with HDA using standard primers. Thus, SAMRS-HDA is a more versatile approach than standard HDA, with a broader applicability for xNA-targeted diagnostics and research.

Detecting respiratory viral RNA using expanded genetic alphabets and self-avoiding DNA.

Nucleic acid (NA)-targeted tests detect and quantify viral DNA and RNA (collectively xNA) to support epidemiological surveillance and, in individual patients, to guide therapy. They commonly use polymerase chain reaction (PCR) and reverse transcription PCR. Although these all have rapid turnaround, they are expensive to run. Multiplexing would allow their cost to be spread over multiple targets, but often only with lower sensitivity and accuracy, noise, false positives, and false negatives; these arise by interactions between the multiple nucleic acid primers and probes in a multiplexed kit. Here we offer a multiplexed assay for a panel of respiratory viruses that mitigates these problems by combining several nucleic acid analogs from the emerging field of synthetic biology: (i) self-avoiding molecular recognition systems (SAMRSs), which facilitate multiplexing, and (ii) artificially expanded genetic information systems (AEGISs), which enable low-noise PCR. These are supplemented by "transliteration" technology, which converts standard nucleotides in a target to AEGIS nucleotides in a product, improving hybridization. The combination supports a multiplexed Luminex-based respiratory panel that potentially differentiates influenza viruses A and B, respiratory syncytial virus, severe acute respiratory syndrome coronavirus (SARS), and Middle East respiratory syndrome (MERS) coronavirus, detecting as few as 10 MERS virions in a 20-µl sample.

A Crystal Structure of a Functional RNA Molecule Containing an Artificial Nucleobase Pair.

As one of its goals, synthetic biology seeks to increase the number of building blocks in nucleic acids. While efforts towards this goal are well advanced for DNA, they have hardly begun for RNA. Herein, we present a crystal structure for an RNA riboswitch where a stem C:G pair has been replaced by a pair between two components of an artificially expanded genetic-information system (AEGIS), Z and P, (6-amino-5-nitro-2(1H)-pyridone and 2-amino-imidazo[1,2-a]-1,3,5-triazin-4-(8H)-one). The structure shows that the Z:P pair does not greatly change the conformation of the RNA molecule nor the details of its interaction with a hypoxanthine ligand. This was confirmed in solution by in-line probing, which also measured a 3.7 nM affinity of the riboswitch for guanine. These data show that the Z:P pair mimics the natural Watson-Crick geometry in RNA in the first example of a crystal structure of an RNA molecule that contains an orthogonal added nucleobase pair.

Enzyme-assisted high throughput sequencing of an expanded genetic alphabet at single base resolution.

With just four building blocks, low sequence information density, few functional groups, poor control over folding, and difficulties in forming compact folds, natural DNA and RNA have been disappointing platforms from which to evolve receptors, ligands, and catalysts. Accordingly, synthetic biology has created "artificially expanded genetic information systems" (AEGIS) to add nucleotides, functionality, and information density. With the expected improvements seen in AegisBodies and AegisZymes, the task for synthetic biologists shifts to developing for expanded DNA the same analytical tools available to natural DNA. Here we report one of these, an enzyme-assisted sequencing of expanded genetic alphabet (ESEGA) method to sequence six-letter AEGIS DNA. We show how ESEGA analyses this DNA at single base resolution, and applies it to optimized conditions for six-nucleotide PCR, assessing the fidelity of various DNA polymerases, and extending this to AEGIS components with functional groups. This supports the renewed exploitation of expanded DNA alphabets in biotechnology.

Harnessing non-standard nucleic acids for highly sensitive icosaplex (20-plex) detection of microbial threats.

Environmental surveillance and clinical diagnostics heavily rely on the polymerase chain reaction (PCR) for target detection. A growing list of microbial threats warrants new PCR-based detection methods that are highly sensitive, specific, and multiplexable. Here, we introduce a PCR-based icosaplex (20-plex) assay for detecting 18 enteropathogen and two antimicrobial resistance genes. This multiplexed PCR assay leverages the self-avoiding molecular recognition system (SAMRS) to avoid primer dimer formation, the artificially expanded genetic information system (AEGIS) for amplification specificity, and next-generation sequencing for amplicon identification. We benchmarked this assay using a low-cost, portable sequencing platform (Oxford Nanopore) on wastewater, soil, and human stool samples. Using parallelized multi-target TaqMan Array Cards (TAC) to benchmark performance of the 20-plex assay, there was 74% agreement on positive calls and 97% agreement on negative calls. Additionally, we show how sequencing information from the 20-plex can be used to further classify allelic variants of genes and distinguish sub-species. The strategy presented offers sensitive, affordable, and robust multiplex detection that can be used to support efforts in wastewater-based epidemiology, environmental monitoring, and human/animal diagnostics.

A folding motif formed with an expanded genetic alphabet.

Adding synthetic nucleotides to DNA increases the linear information density of DNA molecules. Here we report that it also can increase the diversity of their three-dimensional folds. Specifically, an additional nucleotide (dZ, with a 5-nitro-6-aminopyridone nucleobase), placed at twelve sites in a 23-nucleotides-long DNA strand, creates a fairly stable unimolecular structure (that is, the folded Z-motif, or fZ-motif) that melts at 66.5 °C at pH 8.5. Spectroscopic, gel and two-dimensional NMR analyses show that the folded Z-motif is held together by six reverse skinny dZ-:dZ base pairs, analogous to the crystal structure of the free heterocycle. Fluorescence tagging shows that the dZ-:dZ pairs join parallel strands in a four-stranded compact down-up-down-up fold. These have two possible structures: one with intercalated dZ-:dZ base pairs, the second without intercalation. The intercalated structure would resemble the i-motif formed by dC:dC+-reversed pairing at pH ≤ 6.5. This fZ-motif may therefore help DNA form compact structures needed for binding and catalysis.

Conversion strategy using an expanded genetic alphabet to assay nucleic acids.

Methods to detect DNA and RNA (collectively xNA) are easily plagued by noise, false positives, and false negatives, especially with increasing levels of multiplexing in complex assay mixtures. Here, we describe assay architectures that mitigate these problems by converting standard xNA analyte sequences into sequences that incorporate nonstandard nucleotides (Z and P). Z and P are extra DNA building blocks that form tight nonstandard base pairs without cross-binding to natural oligonucleotides containing G, A, C, and T (GACT). The resulting improvements are assessed in an assay that inverts the standard Luminex xTAG architecture, placing a biotin on a primer (rather than on a triphosphate). This primer is extended on the target to create a standard GACT extension product that is captured by a CTGA oligonucleotide attached to a Luminex bead. By using conversion, a polymerase incorporates dZTP opposite template dG in the absence of dCTP. This creates a Z-containing extension product that is captured by a bead-bound oligonucleotide containing P, which binds selectively to Z. The assay with conversion produces higher signals than the assay without conversion, possibly because the Z/P pair is stronger than the C/G pair. These architectures improve the ability of the Luminex instruments to detect xNA analytes, producing higher signals without the possibility of competition from any natural oligonucleotides, even in complex biological samples.

Recognition of an expanded genetic alphabet by type-II restriction endonucleases and their application to analyze polymerase fidelity.

To explore the possibility of using restriction enzymes in a synthetic biology based on artificially expanded genetic information systems (AEGIS), 24 type-II restriction endonucleases (REases) were challenged to digest DNA duplexes containing recognition sites where individual Cs and Gs were replaced by the AEGIS nucleotides Z and P [respectively, 6-amino-5-nitro-3-(1'-ß-D-2'-deoxyribofuranosyl)-2(1H)-pyridone and 2-amino-8-(1'-ß-D-2'-deoxyribofuranosyl)-imidazo[1,2-a]-1,3,5-triazin-4(8H)-one]. These AEGIS nucleotides implement complementary hydrogen bond donor-donor-acceptor and acceptor-acceptor-donor patterns. Results allowed us to classify type-II REases into five groups based on their performance, and to infer some specifics of their interactions with functional groups in the major and minor grooves of the target DNA. For three enzymes among these 24 where crystal structures are available (BcnI, EcoO109I and NotI), these interactions were modeled. Further, we applied a type-II REase to quantitate the fidelity polymerases challenged to maintain in a DNA duplex C:G, T:A and Z:P pairs through repetitive PCR cycles. This work thus adds tools that are able to manipulate this expanded genetic alphabet in vitro, provides some structural insights into the working of restriction enzymes, and offers some preliminary data needed to take the next step in synthetic biology to use an artificial genetic system inside of living bacterial cells.

Enzyme-Assisted High Throughput Sequencing of an Expanded Genetic Alphabet at Single Base Resolution.

Many efforts have sought to apply laboratory in vitro evolution (LIVE) to natural nucleic acid (NA) scaffolds to directly evolve functional molecules. However, synthetic biology can move beyond natural NA scaffolds to create molecular systems whose libraries are far richer reservoirs of functionality than natural NAs. For example, "artificially expanded genetic information systems" (AEGIS) add up to eight nucleotides to the four found in standard NA. Even in its simplest 6-letter versions, AEGIS adds functional groups, information density, and folding motifs that natural NA libraries lack. To complete this vision, however, tools are needed to sequence molecules that are created by AEGIS LIVE. Previous sequencing approaches, including approaches from our laboratories, exhibited limited performance and lost many sequences in diverse library mixtures. Here, we present a new approach that enzymatically transforms the target AEGIS DNA. With higher transliteration efficiency and fidelity, this Enzyme-Assisted Sequencing of Expanded Genetic Alphabet (ESEGA) approach produces substantially better sequences of 6-letter (AGCTZP) DNA than previous transliteration approaches. Therefore, ESEGA facilitates precise analysis of libraries, allowing 'next-generation deep sequencing' to accurately quantify the sequences of 6-letter DNA molecules at single base resolution. We then applied ESEGA to three tasks: (a) defining optimal conditions to perform 6-nucleotide PCR (b) evaluating the fidelity of 6-nucleotide PCR with various DNA polymerases, and (c) extending that evaluation to AEGIS components functionalized with alkynyl and aromatic groups. No other approach at present has this scope, allowing this work to be the next step towards exploiting the potential of expanded DNA alphabets in biotechnology.

Amplification, mutation, and sequencing of a six-letter synthetic genetic system.

The next goals in the development of a synthetic biology that uses artificial genetic systems will require chemistry-biology combinations that allow the amplification of DNA containing any number of sequential and nonsequential nonstandard nucleotides. This amplification must ensure that the nonstandard nucleotides are not unidirectionally lost during PCR amplification (unidirectional loss would cause the artificial system to revert to an all-natural genetic system). Further, technology is needed to sequence artificial genetic DNA molecules. The work reported here meets all three of these goals for a six-letter artificially expanded genetic information system (AEGIS) that comprises four standard nucleotides (G, A, C, and T) and two additional nonstandard nucleotides (Z and P). We report polymerases and PCR conditions that amplify a wide range of GACTZP DNA sequences having multiple consecutive unnatural synthetic genetic components with low (0.2% per theoretical cycle) levels of mutation. We demonstrate that residual mutation processes both introduce and remove unnatural nucleotides, allowing the artificial genetic system to evolve as such, rather than revert to a wholly natural system. We then show that mechanisms for these residual mutation processes can be exploited in a strategy to sequence "six-letter" GACTZP DNA. These are all not yet reported for any other synthetic genetic system.

Synthetic Biology, Tinkering Biology, and Artificial Biology. What are We Learning?

While chemical theory cannot yet support an engineering vision that allows molecules, DNA sequences, and proteins to be interchangeable parts in artificial constructs without "tinkering", progress can be made in synthetic biology by pursuing challenges at the limits of existing theory. These force scientists across uncharted terrain where they must address unscripted problems where, if theory is inadequate, failure results. Thus, synthesis drives discovery and paradigm change in ways that analysis cannot. Further, if failures are analyzed, new theories emerge. Here, we illustrate this by synthesizing an artificial genetic system capable of Darwinian evolution, a feature theorized to be universal to life.

Ultra-rapid detection of SARS-CoV-2 in public workspace environments.

Managing the pandemic caused by SARS-CoV-2 requires new capabilities in testing, including the possibility of identifying, in minutes, infected individuals as they enter spaces where they must congregate in a functioning society, including workspaces, schools, points of entry, and commercial business establishments. Here, the only useful tests (a) require no sample transport, (b) require minimal sample manipulation, (c) can be performed by unlicensed individuals, (d) return results on the spot in much less than one hour, and (e) cost no more than a few dollars. The sensitivity need not be as high as normally required by the FDA for screening asymptomatic carriers (as few as 10 virions per sample), as these viral loads are almost certainly not high enough for an individual to present a risk for forward infection. This allows tests specifically useful for this pandemic to trade-off unneeded sensitivity for necessary speed, simplicity, and frugality. In some studies, it was shown that viral load that creates forward-infection risk may exceed 105 virions per milliliter, easily within the sensitivity of an RNA amplification architecture, but unattainable by antibody-based architectures that simply target viral antigens. Here, we describe such a test based on a displaceable probe loop amplification architecture.