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- BS in Recombinant Genetics and Computer Science. Western Kentucky University (2000)
Role at the Foundation
- Software Engineering. As a cutting-edge research organization, the FfAME requires custom software that can perform duties such as unique primer creation, sequence analysis, and analysis of large amounts of biological data. I am in charge of creating this software, as well as maintaining a large-scale database to house both internally and externally created data that is integral to our research.
- Data Analysis. Working with the scientists at FfAME, I assist in analyzing data using custom-made and 3rd-party tools. This includes such data as high-throughput sequencing, protein heterogeneity, and pathogen strain relatedness.
- IT Management. Serving as the Foundation's IT manager, I am responsible for the setup and maintenance of the Foundation.s servers, as well as a 16-node computer cluster. I am also tasked with assisting FfAME employees with personal workstation setup, software installation, and troubleshooting any computer-related issues.
In vitro evolution of ribonucleases from expanded genetic alphabets
Jerome, C.A; Hoshika, S.; Bradley, K.M.; Benner, S.A.; Biondi, E.
Proc. Natl. Acad. Sci. USA
(2022) 119(44). DOI: 10.1073/pnas.2208261119
The ability of nucleic acids to catalyze reactions (as well as store and transmit information) is important for both basic and applied science, the first in the context of molecular evolution and the origin of life and the second for biomedical applications. However, the catalytic power of standard nucleic acids (NAs) assembled from just four nucleotide building blocks is limited when compared with that of proteins. Here, we assess the evolutionary potential of libraries of nucleic acids with six nucleotide building blocks as reservoirs for catalysis. We compare the outcomes of in vitro selection experiments toward RNA-cleavage activity of two nucleic acid libraries: one built from the standard four independently replicable nucleotides and the other from six, with the two added nucleotides coming from an artificially expanded genetic information system (AEGIS). Results from comparative experiments suggest that DNA libraries with increased chemical diversity, higher information density, and larger searchable sequence spaces are one order of magnitude richer reservoirs of molecules that catalyze the cleavage of a phosphodiester bond in RNA than DNA libraries built from a standard four-nucleotide alphabet. Evolved AEGISzymes with nitro-carrying nucleobase Z appear to exploit a general acid–base catalytic mechanism to cleave that bond, analogous to the mechanism of the ribonuclease A family of protein enzymes and heavily modified DNAzymes. The AEGISzyme described here represents a new type of catalysts evolved from libraries built from expanded genetic alphabets.
Ultra-rapid detection of SARS-CoV-2 in public workspace environments
Yaren, O., McCarter, J., Phadke, N., Bradley, K. M., Overton, B., Yang, Z., Ranade, S., Patil, K., Bangale, R., Benner, S. A.
, Public Library of Science (2021) 10.1371/journal.pone.0240524, DOI:10.1101/2020.09.29.20204131
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.
Eliminating Primer Dimers and Improving SNP detection using Self-Avoiding Molecular Recognition Systems (SAMRS)
Yang, Z., Le, J.T., Hutter, D., Bradley, K.M., Overton, B.R., McLendon, C., Benner, S.A.
Biol. Methods Protoc.
, Oxford Academics (2020) 5(1):bpaa004, DOI:10.1093/biomethods/bpaa004
Despite its widespread value to molecular biology, the polymerase chain reaction (PCR) encounters modes that unproductively consume PCR resources and prevent clean signals, especially when high sensitivity, high SNP discrimination, and high multiplexing are sought. Here, we show how "self-avoiding molecular recognition systems" (SAMRS) manage such difficulties. SAMRS nucleobases pair with complementary nucleotides with strengths comparable to the A:T pair, but do not pair with other SAMRS nucleobases. This should allow primers holding SAMRS components to avoid primer-primer interactions, preventing primer dimers, allowing more sensitive SNP detection, and supporting higher levels of multiplex PCR. The experiments here examine the PCR performances of primers containing different numbers of SAMRS components placed strategically at different positions, and put these performances in the context of estimates of SAMRS:standard pairing strengths. The impact of these variables on primer dimer formation, the overall efficiency and sensitivity of SAMRS-based PCR, and the value of SAMRS primers when detecting single nucleotide polymorphisms (SNPs) are also evaluated. With appropriately chosen polymerases, SNP discrimination can be greater than the conventional allele-specific PCR, with the further benefit of avoiding primer dimer artifacts. General rules guiding the design of SAMRS-modified primers are offered to support medical research and clinical diagnostics products.
Multiplexed kit based on Luminex technology and achievements in synthetic biology discriminates Zika, chikungunya, and and four serotypes of dengue viruses in mosquitoes.
Glushakova, L.G.. Alto, B.W., Kim, M.-S., Hutter, D., Bradley, A., Bradley, K.M., Burkett-Cadena, N.D., Benner, S.A.
BMC Infect. Dis.
, BioMed Central Ltd. (2019) 19:418, DOI:10.1186/s12879-019-3998-z
The global expansion of dengue (DENV), chikungunya (CHIKV), and Zika viruses (ZIKV) is having a serious impact on public health. Because these arboviruses are transmitted by the same mosquito species and co-circulate in the same area, a sensitive diagnostic assay that detects them together, with discrimination, is needed.
We present here a diagnostics panel based on reverse transcription-PCR amplification of viral RNA and an xMap Luminex architecture involving direct hybridization of PCRamplicons and virus-specific probes. Two DNA innovations ("artificially expanded genetic information systems", AEGIS, and "self-avoiding molecular recognition systems", SAMRS) increase the hybridization sensitivity on Luminex microspheres and PCR specificity of the multiplex assay compared to the standard approach (standard nucleotides).
The diagnostics panel detects, if they are present, these viruses with a resolution of 20 genome equivalents (DENV1), or 10 (DENV3-4, CHIKV) and 80 (DENV2, ZIKV) genome equivalents per assay. It identifies ZIKV, CHIKV and DENV RNAs in a single infected mosquito, in mosquito pools comprised of 5 to 50 individuals, and mosquito saliva (ZIKV, CHIKV, and DENV2). Infected mosquitoes and saliva were also collected on a cationic surface (Q-paper), which binds mosquito and viral nucleic acids electrostatically. All samples from infected mosquitoes displayed only target-specific signals; signals from non-infected samples were at background levels.
Our results provide an efficient and multiplex tool that may be used for surveillance of emerging mosquito-borne pathogens which aids targeted mosquito control in areas at high risk for transmission.
Multiplexed isothermal amplification based diagnostic platform to detect Zika, chikungunya, and dengue-1.
Yaren, O., Alto, B. W., Bradley, K. M., Moussatche, P., Benner, S. A.
J. Vis. Exp.
, JoVE (2018) 133: e57051, DOI:10.3791/57051
Zika, dengue, and chikungunya viruses are transmitted by mosquitoes, causing diseases with similar patient symptoms. However, they have different downstream patient-to-patient transmission potentials, and require very different patient treatments. Thus, recent Zika outbreaks make it urgent to develop tools that rapidly discriminate these viruses in patients and trapped mosquitoes, to select the correct patient treatment, and to understand and manage their epidemiology in real time. Unfortunately, current diagnostic tests, including those receiving 2016 emergency use authorizations and fast-track status, detect viral RNA by reverse transcription polymerase chain reaction (RT-PCR), which requires instrumentation, trained users, and considerable sample preparation. Thus, they must be sent to "approved" reference laboratories, requiring time. Indeed, in August 2016, the Center for Disease Control (CDC) was asking pregnant women who had been bitten by a mosquito and developed a Zika-indicating rash to wait an unacceptable 2 to 4 weeks before learning whether they were infected. We very much need tests that can be done on site, with few resources, and by trained but not necessarily licensed personnel. This video demonstrates an assay that meets these specifications, working with urine or serum (for patients) or crushed mosquito carcasses (for environmental surveillance), all without much sample preparation. Mosquito carcasses are captured on paper carrying quaternary ammonium groups (Q-paper) followed by ammonia treatment to manage biohazards. These are then directly, without RNA isolation, put into assay tubes containing freeze-dried reagents that need no chain of refrigeration. A modified form of reverse transcription loop-mediated isothermal amplification with target-specific fluorescently tagged displaceable probes produces readout, in 30 min, as a three-color fluorescence signal. This is visualized with a handheld, battery-powered device with an orange filter. Forward contamination is prevented with sealed tubes, and the use of thermolabile uracil DNA glycosylase (UDG) in the presence of dUTP in the amplification mixture.
Nucleoside analogs to manage sequence divergence in nucleic acid amplification and SNP detection.
Yang, Z., Kim, H.-J., Le, J., McLendon, C., Bradley, K.M., Kim, M.-S., Hutter, D., Hoshika, S., Yaren, O., Benner, S.A.
Nucl. Acids Res.
(2018) 46(12): 5902-10,DOI:10.1093/nar/gky392
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.
Point of sampling detection of Zika virus within a multiplexed kit capable of detecting dengue and chikungunya
Yaren, O., Alto, B.W., Gangodkar, P.V., Ranade, S.R., Patil, K.N., Bradley, K.M., Yang, Z., Phadke, N., Benner, S.A
BMC Infect. Dis.
, BioMed Central Ltd. (2017) 17(1):293, DOI:10.1186/s12879-017-2382-0
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.
Synthesis and Enzymology of 2'-Deoxy-7-deazaisoguanosine Triphosphate and Its Complement: A Second Generation Pair in an Artificially Expanded Genetic Information System
Karalkar NB, Leal NA, Kim MS, Bradley KM, Benner SA
ACS Synthetic Biology
, American Chemical Society (2016) doi: 10.1021/acssynbio.5b00276
As with natural nucleic acids, pairing between artificial nucleotides can be influenced by tautomerism, with different placements of protons on the heterocyclic nucleobase changing patterns of hydrogen bonding that determine replication fidelity. For example, the major tautomer of isoguanine presents a hydrogen bonding donor-donor-acceptor pattern complementary to the acceptor-acceptor-donor pattern of 5-methylisocytosine. However, in its minor tautomer, isoguanine presents a hydrogen bond donor-acceptor-donor pattern complementary to thymine. Calculations, crystallography, and physical organic experiments suggest that this tautomeric ambiguity might be "fixed" by replacing the N-7 nitrogen of isoguanine by a CH unit. To test this hypothesis, we prepared the triphosphate of 2'-deoxy-7-deazaiso-guanosine and used it in PCR to estimate an effective tautomeric ratio "seen" by Taq DNA polymerase. With 7-deazaisoguanine, fidelity-per-round was ~92%. The analogous PCR with isoguanine gave a lower fidelity-per-round of ~86%. These results confirm the hypothesis with polymerases, and deepen our understanding of the role of minor groove hydrogen bonding and proton tautomerism in both natural and expanded genetic "alphabets", major targets in synthetic biology.
Aptamers against Cells Overexpressing Glypican 3 from Expanded
Genetic Systems Combined with Cell Engineering and Laboratory
Zhang, L, Yang, Z, Trinh, TL, Teng, I-T, Wang, S, Bradley, KM, Hoshika, S, Wu, Q, Cansiz, S, Rowold, DJ, McLendon, C, Kim, M-S, Wu, Y, Cui, C, Liu, Y, Hou, W, Stewart, K, Wan, S, Liu, C, Benner, SA, Tan, W
Angew. Chem. Int. Ed.
55 (2016) doi: 10.1002/anie.201605058
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 sixletter
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 selectionâ€“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.
Standard and AEGIS nicking molecular beacons detect amplicons from the Middle East respiratory syndrome coronavirus
Ozlem Yaren, Lyudmyla G. Glushakova, Kevin M. Bradley, Shuichi Hoshika,Steven A. Benner
J Virol Methods
(236) , Elsevier 54-61 (2016) doi:10.1016/j.jviromet.2016.07.008
This paper combines two advances to detect MERS-CoV, the causative agent of Middle East Respiratory Syndrome, that have emerged over the past few years from the new field of "synthetic biology". Both are based on an older concept, where molecular beacons are used as the downstream detection of viral RNA in biological mixtures followed by reverse transcription PCR amplification. The first advance exploits the artificially expanded genetic information systems (AEGIS). AEGIS adds nucleotides to the four found in standard DNA and RNA (xNA); AEGIS nucleotides pair orthogonally to the A:T and G:C pairs. Placing AEGIS components in the stems of molecular beacons is shown to lower noise by preventing unwanted stem invasion by adventitious natural xNA. This should improve the signal-to-noise ratio of molecular beacons operating in complex biological mixtures. The second advance introduces a nicking enzyme that allows a single target molecule to activate more than one beacon, allowing "signal amplification". Combining these technologies in primers with components of a self-avoiding molecular recognition system (SAMRS), we detect 50 copies of MERS-CoV RNA in a multiplexed respiratory virus panel by generating fluorescence signal visible to human eye and/or camera.
(View publication page for Kevin Bradley)
- High-throughput sequence analysis
- Large-scale database design
- Software engineering
- Web-based collaborative applications