Bisulfite sequencing detects 5mC and 5hmC at single-base resolution. However, bisulfite treatment damages DNA, which results in fragmentation, DNA loss, and biased sequencing data. To overcome these problems, enzymatic methyl-seq (EM-seq) was developed. This method detects 5mC and 5hmC using two sets of enzymatic reactions. In the first reaction, TET2 and T4-BGT convert 5mC and 5hmC into products that cannot be deaminated by APOBEC3A. In the second reaction, APOBEC3A deaminates unmodified cytosines by converting them to uracils. Therefore, these three enzymes enable the identification of 5mC and 5hmC. EM-seq libraries were compared with bisulfite-converted DNA, and each library type was ligated to Illumina adaptors before conversion. Libraries were made using NA12878 genomic DNA, cell-free DNA, and FFPE DNA over a range of DNA inputs. The 5mC and 5hmC detected in EM-seq libraries were similar to those of bisulfite libraries. However, libraries made using EM-seq outperformed bisulfite-converted libraries in all specific measures examined (coverage, duplication, sensitivity, etc.). EM-seq libraries displayed even GC distribution, better correlations across DNA inputs, increased numbers of CpGs within genomic features, and accuracy of cytosine methylation calls. EM-seq was effective using as little as 100 pg of DNA, and these libraries maintained the described advantages over bisulfite sequencing. EMseq library construction, using challenging samples and lower DNA inputs, opens new avenues for research and clinical applications.

The enzyme isopenicillin N synthase (IPNS) installs the β-lactam and thiazolidine rings of the penicillin core into the linear tripeptide, L-δ-aminoadipoyl-L-Cys-D-Val (ACV), on the pathways to a number of important antibacterial drugs. A classic set of enzymological and crystallographic studies by Baldwin and co-workers established that this overall four-electron oxidation occurs by a sequence of two oxidative cyclizations, with the β-lactam ring being installed first and the thiazolidine ring second. Each phase requires cleavage of an aliphatic C–H bond of the substrate: the pro-S-CCys,β-H bond for closure of the β-lactam ring, and the CVal,β-H bond for installation of the thiazolidine ring. IPNS uses a mononuclear non-heme-iron(II) cofactor and dioxygen as co-substrate to cleave these C–H bonds and direct the ring closures. Despite the intense scrutiny to which the enzyme has been subjected, the identities of the oxidized iron intermediates that cleave the C–H bonds have been addressed only computationally; no experimental insight into their geometric or electronic structures has been reported. In this work, we have employed a combination of transient-state-kinetic and spectroscopic methods, together with the specifically deuterium-labeled substrates, A[d2-C]V and AC[d8-V], to identify both C–H-cleaving intermediates. The results show that they are high-spin Fe(III)-superoxo and high-spin Fe(IV)-oxo complexes, respectively, in agreement with published mechanistic proposals derived computationally from Baldwin’s founding work.

Modified DNA bases in mammalian genomes, such as 5-methylcytosine ( 5m C) and its oxidized forms, are implicated in important epigenetic regulation processes. In human or mouse, successive enzymatic conversion of 5m C to its oxidized forms is carried out by the ten-eleven translocation (TET) proteins. Previously we reported the structure of a TET-like 5m C oxygenase (NgTET1) from Naegleria gruberi, a single-celled protist evolutionarily distant from vertebrates. Here we show that NgTET1 is a 5-methylpyrimidine oxygenase, with activity on both 5m C (major activity) and thymidine (T) (minor activity) in all DNA forms tested, and provide unprecedented evidence for the formation of 5-formyluridine ( 5f U) and 5-carboxyuridine ( 5ca U) in vitro. Mutagenesis studies reveal a delicate balance between choice of 5m C or T as the preferred substrate. Furthermore, our results suggest substrate preference by NgTET1 to 5m CpG and TpG dinucleotide sites in DNA. Intriguingly, NgTET1 displays higher T-oxidation activity in vitro than mammalian TET1, supporting a closer evolutionary relationship between NgTET1 and the base J-binding proteins from trypanosomes. Finally, we demonstrate that NgTET1 can be readily used as a tool in 5m C sequencing technologies such as single molecule, realtime sequencing to map 5m C in bacterial genomes at base resolution.odified DNA bases exist in all forms of life, from viruses to mammals with many different biological roles. Accordingly, diverse mechanisms have evolved to "write," "read," and "erase" these modifications. In mammals, 5-methylcytosine ( 5m C) is the major form of DNA modification and is implicated in many crucial developmental processes. In human and mouse, 5m C can be successively oxidized into 5-hydroxymethylcytosine ( 5hm C), 5-formylcytosine ( 5f C), and 5-carboxylcytosine ( 5ca C) by the teneleven translocation (TET) family of oxygenases (1-4). The bases of 5f C and 5ca C can be excised by thymine DNA glycosylase (4). The 5m C-oxidation-coupled base-excision repair pathway provides a plausible route for active demethylation in mammalian cells. Many other species, from simple to complex, maintain DNA methylation machinery throughout their life cycle that may contribute to epigenetic regulation. Therefore, an interesting perspective is to examine shared and distinct features of TET oxygenases in diverse eukaryotes (5, 6).The human and mouse genomes encode three paralogous TET proteins, TET1, TET2, and TET3, which presumably carry out both redundant and distinct functions (7,8). TET proteins belong to the diverse group of α-ketoglutarate (αKG) and Fe(II)-dependent oxygenases (5). Subgroup classification based on sequence similarity links the TET proteins to base J-binding proteins (JBP1 and JBP2), which are primarily present in trypanosomes and possess thymidine (T)-hydroxylation activity (1). Further bioinformatic analysis revealed eight paralogous TET/ JBP-like genes in the genome of Naegleria gruberi, a single-celled amoeboflagellate protist that is a distant cousin of the par...

Bisulfite sequencing is widely used to detect 5mC and 5hmC at single base resolution. It is the most accepted method for detecting these cytosine modifications, but it does have significant drawbacks. DNA is frequently damaged resulting in fragmentation, loss of DNA and inherent biases introduced to sequencing data. To overcome this, we developed a new method called Enzymatic Methyl-seq (EMseq). This method relies on two sets of enzymatic reactions. In the first reaction, TET2 and T4-bGT convert 5mC and 5hmC into substrates that cannot be deaminated by APOBEC3A. In the second reaction, APOBEC3A deaminates unmodified cytosines converting them to uracils. The protection of 5mC and 5hmC permits the discrimination of cytosines from 5mC and 5hmC. Over a range of DNA inputs, the overall fraction of 5mC and 5hmC in EM-seq libraries was similar to bisulfite libraries. However, libraries made using EM-seq outperformed bisulfite converted libraries in all specificmeasures examined including coverage, duplication, sensitivity and nucleotide composition. EM-seq libraries displayed even GC distribution, improved correlation across input amounts, increased numbers of CpGs confidently assessed within genomic features, and improved the accuracy of cytosine methylation calls in other contexts. Bisulfite sequencing is known to severely damage DNA thus making library construction for lower DNA input very difficult. We show that EM-seq can be used to make libraries using as little as 100 pg of DNA. These libraries maintain all of the previously described advantages over bisulfite sequencing thus opening new avenues for research and clinical applications. Even with challenging input material, EM-seq provides a method to detect methylation state more reliably than WBGS.[7]. Sequencing distinguishes cytosines from these modified forms as they are read as thymines and cytosines respectively [8]. Despite its widespread use amongst epigenetic researchers, bisulfite sequencing also has significant drawbacks. It requires extreme temperatures and pH which causes depyrimidination of DNA resulting in DNA degradation [9]. Furthermore, cytosines are damaged disproportionately compared to 5mC or 5hmC. As a result, sequencing libraries made from converted DNA have an unbalanced nucleotide composition. All of these issues taken together result in libraries with reduced mapping rates and skewed GC bias plots, with a general under-representation of G-and Ccontaining dinucleotides and over-representation of AA-, AT-and TA-containing dinucleotides, when compared to a non-converted genome [10]. Therefore, the damaged libraries do not adequately cover the genome, and can include many gaps with little or no coverage. Increasing the sequencing depth of these libraries may recover some missing information, but at steep sequencing costs.These bisulfite library limitations have driven the development of new approaches for mapping 5mC and 5hmC, in combination or independently, for epigenome analysis. The methylation dependent restriction enzymes (MDRE), MspJI ...

The ten-eleven translocation (TET) proteins catalyze oxidation of 5-methylcytosine ((5m)C) residues in nucleic acids to 5-hydroxymethylcytosine ((5hm)C), 5-formylcytosine ((5f)C), and 5-carboxycytosine ((5ca)C). These nucleotide bases have been implicated as intermediates on the path to active demethylation, but recent reports have suggested that they might have specific regulatory roles in their own right. In this study, we present kinetic evidence showing that the catalytic domains (CDs) of TET2 and TET1 from mouse and their homologue from Naegleria gruberi, the full-length protein NgTET1, are distributive in both chemical and physical senses, as they carry out successive oxidations of a single (5m)C and multiple (5m)C residues along a polymethylated DNA substrate. We present data showing that the enzyme neither retains (5hm)C/(5f)C intermediates of preceding oxidations nor slides along a DNA substrate (without releasing it) to process an adjacent (5m)C residue. These findings contradict a recent report by Crawford et al. ( J. Am. Chem. Soc. 2016 , 138 , 730 ) claiming that oxidation of (5m)C by CD of mouse TET2 is chemically processive (iterative). We further elaborate that this distributive mechanism is maintained for TETs in two evolutionarily distant homologues and posit that this mode of function allows the introduction of (5m)C forms as epigenetic markers along the DNA.

The ongoing SARS-CoV-2 pandemic has necessitated a dramatic increase in our ability to conduct molecular diagnostic tests, as accurate detection of the virus is critical in preventing its spread. However, SARS-CoV-2 variants continue to emerge, with each new variant potentially affecting widely-used nucleic acid amplification diagnostic tests. RT-LAMP has been adopted as a quick, inexpensive diagnostic alternative to RT-qPCR, but as a newer method, has not been studied as thoroughly. Here we interrogate the effect of SARS-CoV-2 sequence mutations on RT-LAMP amplification, creating 523 single point mutation “variants” covering every position of the LAMP primers in 3 SARS-CoV-2 assays and analyzing their effects with over 4,500 RT-LAMP reactions. Remarkably, we observed only minimal effects on amplification speed and no effect on detection sensitivity at positions equivalent to those that significantly impact RT-qPCR assays. We also created primer sets targeting a specific short deletion and observed that LAMP is able to amplify even with a primer containing multiple consecutive mismatched bases, albeit with reduced speed and sensitivity. This highlights RT-LAMP as a robust technique for viral RNA detection that can tolerate most mutations in the primer regions. Additionally, where variant discrimination is desired, we describe the use of molecular beacons to sensitively distinguish and identify variant RNA sequences carrying short deletions. Together these data add to the growing body of knowledge on the utility of RT-LAMP and increase its potential to further our ability to conduct molecular diagnostic tests outside of the traditional clinical laboratory environment.

DNA isolated from blood draws (cell-free DNA (cfDNA)) or from archival material like formalin fixed paraffin embedded (FFPE) tissues have advanced the field of cancer genetics. DNA methylation (5-methylcytosines (5mC) and 5-hydroxymethylcytosines (5hmC)) is a key epigenetic factor that plays an important role in cellular processes and it’s misregulation results in diseased states like cancer. Advances in the field of sample preparation from biological matrices and genomics have enabled cancer biomarker identification based on methylation profiling. Bisulfite sequencing is the standard method to detect methylation and has been employed for both targeted and whole genome methylation analysis. However, the chemical based bisulfite conversion of cytosines to uracils also results in DNA damage which subsequently results in shorter DNA insert sizes as well as introducing bias into the data. Robust biomarker detection relies primarily on the ability to profile methylation accurately. Analysis of DNA methylation from cfDNA and FFPE DNA is challenging as the DNA is typically of low quality and quantity. To overcome the drawbacks of bisulfite sequencing, we developed an enzyme based methylation detection technology, called NEBNext Enzymatic Methyl-Seq (EM-Seq). DNA damage is minimized enabling longer insert sizes, lower duplication rates and minimal GC bias resulting in more accurate quantification of methylation in the sample DNA. Using EM-Seq, we profiled cfDNA and FFPE DNA from multiple tissue types. Results for these challenging DNA types showed that the EM-Seq libraries had longer inserts, lower duplication rates, higher percentages of mapped reads and less GC bias compared to WGBS libraries. These libraries also identified a higher number of CpG’s and the estimated global methylation levels were in good agreement with the absolute levels quantified using LC/MS. In conclusion, EM-Seq libraries have superior sequencing metrics resulting in robust methylation profiling for these types of challenging DNA samples. Citation Format: Louise Williams, V K Chaithanya Ponnaluri, Brittany S. Sexton, Lana Saleh, Katherine Marks, Mala Samaranayake, Laurence Ettwiller, Shengxi Guan, Heidi E. Church, Nan Dai, Esta Tamanaha, Erbay Yigit, Bradley Langhorst, Zhiyi Sun, Thomas C. Evans, Romualdas Vaisvila, Eileen Dimalanta, Theodore B. Davis. Enzymatic Methyl-Seq: methylome analysis of challenging DNA samples [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 820.

Prokaryotic Argonautes (pAgo) are an increasingly well-studied class of guided endonucleases, and the underlying mechanisms by which pAgo generate nucleic acid guides in vivo remains an important topic of investigation. Recent insights into these mechanisms for the Argonaute protein from Thermus thermophilus has drawn attention to global sequence and structural feature preferences involved in oligonucleotide guide selection. In this work, we approach the study of guide sequence preferences in T. thermophilus Argonaute from a functional perspective. Screening a library of 1,968 guides against randomized single- and double-stranded DNA substrates, endonuclease activity associated with each guide was quantified using high-throughput capillary electrophoresis, and localized sequence preferences were identified which can be used to improve guide design for molecular applications. The most notable preferences include: a strong cleavage enhancement from a first position dT independent of target sequence; a significant decrease in activity with dA at position 12; and an impact of GC dinucleotides at positions 10 and 11. While this method has been useful in characterizing unique preferences of T. thermophilus Argonaute and criteria for creating efficient guides, it could be expanded further to rapidly characterize more recent mesophilic variants reported in the literature and drive their utility toward molecular tools in biology and genome editing applications.