S-adenosyl-L-methionine Analogues Research Articles

Efficient Transferase Engineering for SAM Analog Synthesis from Iodoalkanes.

S-Adenosyl-l-methionine (SAM) is an important cosubstrate in various biochemical processes, including selective methyl transfer reactions. Simple methods for the (re)generation of SAM analogs could expand the chemistry accessible with SAM-dependent transferases and go beyond methylation reactions. Here we present an efficient enzyme engineering strategy to synthesize different SAM analogs from "off-the-shelf" iodoalkanes through enzymatic alkylation of S-adenosyl-l-homocysteine (SAH). This was achieved by mutating multiple hydrophobic and structurally dynamic amino acids simultaneously. Combinatorial mutagenesis was guided by the natural amino acid diversity and generated a highly functional mutant library. This approach increased the speed as well as the scale of enzyme engineering by providing a panel of optimized enzymes with orders of magnitude higher activities for multiple substrates in just one round of enzyme engineering. The optimized enzymes exhibit catalytic efficiencies up to 31 M-1 s-1, convert various iodoalkanes, including substrates bearing cyclopropyl or aromatic moieties, and catalyze S-alkylation of SAH with very high stereoselectivities (>99 % de). We further report a high throughput chromatographic screening system for reliable and rapid SAM analog analysis. We believe that the methods and enzymes described herein will further advance the field of selective biocatalytic alkylation chemistry by enabling SAM analog regeneration with "off-the-shelf" reagents.

In silico Design of Novel SAM Analogs as Potential Inhibitors Against N2G966 16s rRNA Methyltransferase (RsmD)

Introduction: Tuberculosis (TB), caused by Mycobacterium tuberculosis (M.tb), has its natural history tracing back to 70,000 years. Latent M.tb infection is the reservoir of the TB epidemic. M.tb is becoming more prevalent and acquiring multidrug resistance among the first-line antibiotics. Methods: Methylation is one of the main mechanisms through which bacteria develop resistance, hence targeting methyltransferases provides the opportunity to achieve two-birds-with-one-stone: a) antibiotic: inhibiting the translation activity and b) anti-resistance: eliminating methylation as a mode of resistance. Currently, no known drugs or lead molecules are targeting the methyltransferases, in general, and rRNA Small Subunit Methyltransferase D (RsmD) family, in particular, in M.tb species. Results and Discussion: S-Adenosyl-L-methionine(SAM) is known as the universal donor of a methyl group which is an indispensable cofactor for the proper functioning of SAM-dependent methyltransferases. This in silico study attempts to design and develop novel SAM-analog inhibitors against RsmD, which in turn affects the growth and survival of M.tb in TB patients. The SAM-analogs were designed, after careful study and analysis of RsmD pharmacophore and SAM binding properties. The functional groups such as amide, amine, acetamide, formamide, hydroxyl, fluorine, iodine, and bromine were used to design novel analogs with the aim to improve the binding of analog with RsmD. The analogs that gave better docking scores followed by favourable binding affinities and ADMET properties than native SAM were ranked. Conclusion: Among the library of SAM analogs, the top two analogs with IDs: SAM_172 and SAM_153 need testing and validation for their efficacy through in vitro and in vivo studies.

Enzymatic Synthesis of l-Methionine Analogues and Application in a Methyltransferase Catalysed Alkylation Cascade.

Chemical modification of small molecules is a key step for the development of pharmaceuticals. S-adenosyl-l-methionine (SAM) analogues are used by methyltransferases (MTs) to transfer alkyl, allyl and benzyl moieties chemo-, stereo- and regioselectively onto nucleophilic substrates, enabling an enzymatic way for specific derivatisation of a wide range of molecules. l-Methionine analogues are required for the synthesis of SAM analogues. Most of these are not commercially available. In nature, O-acetyl-l-homoserine sulfhydrolases (OAHS) catalyse the synthesis of l-methionine from O-acetyl-l-homoserine or l-homocysteine, and methyl mercaptan. Here, we investigated the substrate scope of ScOAHS from Saccharomyces cerevisiae for the production of l-methionine analogues from l-homocysteine and organic thiols. The promiscuous enzyme was used to synthesise nine different l-methionine analogues with modifications on the thioether residue up to a conversion of 75 %. ScOAHS was combined with an established MT dependent three-enzyme alkylation cascade, allowing transfer of in total seven moieties onto two MT substrates. For ethylation, conversion was nearly doubled with the new four-enzyme cascade, indicating a beneficial effect of the in situ production of l-methionine analogues with ScOAHS.

Revealing Drivers for Carboxy-S-adenosyl-l-methionine Use by Neomorphic Variants of a DNA Methyltransferase.

Methylation of DNA plays a key role in diverse biological processes spanning from bacteria to mammals. DNA methyltransferases (MTases) typically employ S-adenosyl-l-methionine (SAM) as a critical cosubstrate and the relevant methyl donor for modification of the C5 position of cytosine. Recently, work on the CpG-specific bacterial MTase, M.MpeI, has shown that a single N374K point mutation can confer the enzyme with the neomorphic ability to use the sparse, naturally occurring metabolite carboxy-S-adenosyl-l-methionine (CxSAM) in order to generate the unnatural DNA modification, 5-carboxymethylcytosine (5cxmC). Here, we aimed to investigate the mechanistic basis for this DNA carboxymethyltransferase (CxMTase) activity by employing a combination of computational modeling and in vitro characterization. Modeling of substrate interactions with the enzyme variant allowed us to identify a favorable salt bridge between CxSAM and N374K that helps to rationalize selectivity of the CxMTase. Unexpectedly, we also discovered a potential role for a key active site E45 residue that makes a bidentate interaction with the ribosyl sugar of CxSAM, located on the opposite face of the CxMTase active site. Prompted by these modeling results, we further explored the space-opening E45D mutation and found that the E45D/N374K double mutant in fact inverts selectivity, preferring CxSAM over SAM in biochemical assays. These findings provide new insight into CxMTase active site architecture and may offer broader utility given the numerous opportunities offered by using SAM analogs for selective molecular labeling in concert with nucleic acid or even protein-modifying MTases.

Two-enzyme cascade catalyzed trideuteromethylative modification of natural products

Site-selective incorporation of the trideuterated “magic methyl” group may provide profound pharmacological benefits, which has been considered as an important tool for drug optimization and development in medicinal chemistry. S-adenosyl-L-methionine (SAM) usually acts as the methyl donor under the catalysis of SAM-dependent methyltransferases (MTs), which transfer a methyl group from SAM to substrates, and are widely reported for methylation in natural product biosynthesis. However, it is difficult to introduce other high-value functional groups to substrates in this way since SAM analogs are not easy to obtain in biological methods. Herein we report that trideuterated SAM can be obtained from S-adenosylhomocysterine (SAH) and trideuterated methyl iodide (CD3I) under the participation of halide methyltransferase (HMT). Subsequent one-pot cascades with different MTs achieved the regioselective trideuteromethylation of three natural products, which indicated that trideuterated SAM can be accepted as a co-substrate by C-, N-, O-specific MTs for enzyme-catalyzed trideuteromethylation of natural products.

Potent Inhibition of SARS-CoV-2 nsp14 N7-Methyltransferase by Sulfonamide-Based Bisubstrate Analogues.

Enzymes involved in RNA capping of SARS-CoV-2 are essential for the stability of viral RNA, translation of mRNAs, and virus evasion from innate immunity, making them attractive targets for antiviral agents. In this work, we focused on the design and synthesis of nucleoside-derived inhibitors against the SARS-CoV-2 nsp14 (N7-guanine)-methyltransferase (N7-MTase) that catalyzes the transfer of the methyl group from the S-adenosyl-l-methionine (SAM) cofactor to the N7-guanosine cap. Seven compounds out of 39 SAM analogues showed remarkable double-digit nanomolar inhibitory activity against the N7-MTase nsp14. Molecular docking supported the structure–activity relationships of these inhibitors and a bisubstrate-based mechanism of action. The three most potent inhibitors significantly stabilized nsp14 (ΔTm ≈ 11 °C), and the best inhibitor demonstrated high selectivity for nsp14 over human RNA N7-MTase.

Analogs of S-Adenosyl-L-Methionine in Studies of Methyltransferases.

Methyltransferases (MTases) play an important role in the functioning of living systems, catalyzing the methylation reactions of DNA, RNA, proteins, and small molecules, including endogenous compounds and drugs. Many human diseases are associated with disturbances in the functioning of these enzymes; therefore, the study of MTases is an urgent and important task. Most MTases use the cofactor S‑adenosyl‑L‑methionine (SAM) as a methyl group donor. SAM analogs are widely applicable in the study of MTases: they are used in studies of the catalytic activity of these enzymes, in identification of substrates of new MTases, and for modification of the substrates or substrate linking to MTases. In this review, new synthetic analogs of SAM and the problems that can be solved with their usage are discussed.

Substrate Profiling of Anion Methyltransferases for Promiscuous Synthesis of S-Adenosylmethionine Analogs from Haloalkanes.

Biocatalytic alkylation reactions can be performed with high chemo‐, regio‐ and stereoselectivity using S‐adenosyl‐l‐methionine (SAM)‐dependent methyltransferases (MTs) and SAM analogs. Currently, however, this methodology is limited in application due to the rather laborious protocols to access SAM analogs. It has recently been shown that halide methyltransferases (HMTs) enable synthesis and recycling of SAM analogs with readily available haloalkanes as starting material. Here we expand this work by using substrate profiling of the anion MT enzyme family to explore promiscuous SAM analog synthesis. Our study shows that anion MTs are in general very promiscuous with respect to the alkyl chain as well as the halide leaving group. Substrate profiling further suggests that promiscuous anion MTs cluster in sequence space. Next to iodoalkanes, cheaper, less toxic, and more available bromoalkanes have been converted and several haloalkanes bearing short alkyl groups, alkyl rings, and functional groups such as alkene, alkyne and aromatic moieties are accepted as substrates. Further, we applied the SAM analogs as electrophiles in enzyme‐catalyzed regioselective pyrazole allylation with 3‐bromopropene as starting material.

Analogs of S-Adenosyl-L-Methionine in Studies of Methyltransferases

Methyltransferases (MTases) play an important role in the functioning of living systems, catalyzing the methylation reactions of DNA, RNA, proteins, and small molecules, including endogenous compounds and drugs. Many human diseases are associated with disturbances in the functioning of these enzymes; therefore, the study of MTases is an urgent and important task. Most MTases use the cofactor S-adenosyl-L-methionine (SAM) as a methyl group donor. SAM analogs are widely applicable in the study of MTases: they are used in studies of the catalytic activity of these enzymes, in identification of substrates of new MTases, and for modification of the substrates or substrate linking to MTases. In this review, new synthetic analogs of SAM and the problems that can be solved with their usage are discussed.

Profiling and Validation of Live‐Cell Protein Methylation with Engineered Enzymes and Methionine Analogues

Protein methyltransferases (PMTs) regulate many aspects of normal and disease processes through substrate methylation, with S-adenosyl-L-methionine (SAM) as a cofactor. It has been challenging to elucidate cellular protein lysine and arginine methylation because these modifications barely alter physical properties of target proteins and often are context dependent, transient, and substoichiometric. To reveal bona fide methylation events associated with specific PMT activities in native contexts, we developed the live-cell Bioorthogonal Profiling of Protein Methylation (lcBPPM) technology, in which the substrates of specific PMTs are labeled by engineered PMTs inside living cells, with in situ-synthesized SAM analogues as cofactors. The biorthogonality of this technology is achieved because these SAM analogue cofactors can only be processed by the engineered PMTs-and not native PMTs-to modify the substrates with distinct chemical groups. Here, we describe the latest lcBPPM protocol and its application to reveal proteome-wide methylation and validate specific methylation events. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Live-cell labeling of substrates of protein methyltransferases GLP1 and PRMT1 with lcBPPM-feasible enzymes and SAM analogue precursors Support Protocol: Gram-scale synthesis of Hey-Met Basic Protocol 2: Click labeling of lcBPPM cell lysates with a biotin-azide probe Alternate Protocol: Click labeling of small-scale lcBPPM cell lysates with a TAMRA-azide dye for in-gel fluorescence visualization Basic Protocol 3: Enrichment of biotinylated lcBPPM proteome with streptavidin beads Basic Protocol 4: Proteome-wide identification of lcBPPM targets with mass spectrometry Basic Protocol 5: Validation of individual lcBPPM targets by western blot.

Clostridioides difficile specific DNA adenine methyltransferase CamA squeezes and flips adenine out of DNA helix

Clostridioides difficile infections are an urgent medical problem. The newly discovered C.difficileadenine methyltransferase A (CamA) is specified by all C. difficile genomes sequenced to date (>300), but is rare among other bacteria. CamA is an orphan methyltransferase, unassociated with a restriction endonuclease. CamA-mediated methylation at CAAAAA is required for normal sporulation, biofilm formation, and intestinal colonization by C. difficile. We characterized CamA kinetic parameters, and determined its structure bound to DNA containing the recognition sequence. CamA contains an N-terminal domain for catalyzing methyl transfer, and a C-terminal DNA recognition domain. Major and minor groove DNA contacts in the recognition site involve base-specific hydrogen bonds, van der Waals contacts and the Watson-Crick pairing of a rearranged A:T base pair. These provide sufficient sequence discrimination to ensure high specificity. Finally, the surprisingly weak binding of the methyl donor S-adenosyl-l-methionine (SAM) might provide avenues for inhibiting CamA activity using SAM analogs.

Directed Evolution of a Halide Methyltransferase Enables Biocatalytic Synthesis of Diverse SAM Analogs.

Biocatalytic alkylations are important reactions to obtain chemo‐, regio‐ and stereoselectively alkylated compounds. This can be achieved using S‐adenosyl‐l‐methionine (SAM)‐dependent methyltransferases and SAM analogs. It was recently shown that a halide methyltransferase (HMT) from Chloracidobacterium thermophilum can synthesize SAM from SAH and methyl iodide. We developed an iodide‐based assay for the directed evolution of an HMT from Arabidopsis thaliana and used it to identify a V140T variant that can also accept ethyl‐, propyl‐, and allyl iodide to produce the corresponding SAM analogs (90, 50, and 70 % conversion of 15 mg SAH). The V140T AtHMT was used in one‐pot cascades with O‐methyltransferases (IeOMT or COMT) to achieve the regioselective ethylation of luteolin and allylation of 3,4‐dihydroxybenzaldehyde. While a cascade for the propylation of 3,4‐dihydroxybenzaldehyde gave low conversion, the propyl‐SAH intermediate could be confirmed by NMR spectroscopy.

Fluorescent SAM analogues for methyltransferase based DNA labeling.

In this work, the preparation of new S-adenosyl-l-methionine (SAM) analogues for sequence specific DNA labeling is evaluated. These non-natural analogues, comprising cysteine rather than the natural homolog, were obtained in near quantitative conversions from readily available starting materials without relying on using an excess amount of labor intensive molecules. The synthetic strategy was used to generate fluorescent cofactors, with colours spanning the whole visible spectrum, and their applicability in methyltransferase based optical mapping is shown.

Evaluation of N‐Mustard Analogues of S‐Adenosyl‐L‐methionine with Eukaryotic DNA Methyltransferase 1

AbstractDNA methylation, which requires the universal methyl donor S‐adenosyl‐L‐methionine (SAM), plays a pivotal role in eukaryotic gene regulation and when dysregulated, can result in severe alterations in cellular function. An emerging approach to further understand DNA methylation utilizes azide‐ and alkyne‐functionalized N‐mustard SAM analogues as biochemical tools to probe sites of DNA methylation. While the successful utility of these substituted analogues has been demonstrated with prokaryotic DNA methyltransferases, their utility with physiologically‐relevant eukaryotic DNA methyltransferase 1 (DNMT1) is examined for the first time here. A fluorescence‐based magnetic bead assay was validated in initial experiments to measure the extent of DNA modification by the N‐mustard analogues using Spiroplasma methylase, M.SssI, a prokaryotic model of DNMT1. Subsequent analysis with DNMT1 revealed limited utility of the analogues, as added azide‐ and alkyne‐functionality appears to directly impact binding to DNMT1.

Synthesis of Adenine Dinucleosides 2′,5′‐Bridged by Sulfur‐Containing Linkers as Bisubstrate SAM Analogues for Viral RNA 2′‐O‐Methyltransferases

Viral RNA 2′‐O‐methyltransferases play a crucial role for luring the host cell innate antiviral response during a viral infection by catalyzing either the methylation of the 5′‐end RNA cap‐structure at 2′‐OH of nucleoside N1 or by inducing internal 2′‐O‐methylation of adenosines within RNA sequence using S‐adenosyl‐l‐methionine (SAM) as the methyl donor. Our goal is to synthesize bisubstrate SAM analogues mimicking the transition state of the 2′‐O‐methylation of the RNA in order to block viral 2′‐O‐methyltransferases and struggle against emerging viruses. Here we designed and synthesized five dinucleosides by connecting a 5′‐thioadenosine representing the SAM to the 2′‐OH of another adenosine unit mimicking the RNA substrate, via various sized sulfur‐containing linkers such as alkylthioether linkers, sulfoxide or sulfone derivatives, or a disulfide bond.

Preparation, Assay, and Application of Chlorinase SalL for the Chemoenzymatic Synthesis of S-Adenosyl-l-Methionine and Analogs.

S-adenosyl-l-methionine (SAM) is universal in biology, serving as the second most common cofactor in a variety of enzymatic reactions. One of the main roles of SAM is the methylation of nucleic acids, proteins, and metabolites. Methylation often imparts regulatory control to DNA and proteins, and leads to an increase in the activity of specialized metabolites such as those developed as pharmaceuticals. There has been increased interest in using SAM analogs in methyltransferase-catalyzed modification of biomolecules. However, SAM and its analogs are expensive and unstable, degrading rapidly under physiological conditions. Thus, the availability of methods to prepare SAM in situ is desirable. In addition, synthetic methods to generate SAM analogs suffer from low yields and poor diastereoselectivity. The chlorinase SalL from the marine bacterium Salinispora tropica catalyzes the reversible, nucleophilic attack of chloride at the C5' ribosyl carbon of SAM leading to the formation of 5'-chloro-5'-deoxyadenosine (ClDA) with concomitant displacement of l-methionine. It has been demonstrated that the in vitro equilibrium of the SalL-catalyzed reaction favors the synthesis of SAM. In this chapter, we describe methods for the preparation of SalL, and the chemoenzymatic synthesis of SAM and SAM analogs from ClDA and l-methionine congeners using SalL. In addition, we describe procedures for the in situ chemoenzymatic synthesis of SAM coupled to DNA, peptide, and metabolite methylation, and to the incorporation of isotopes into alkylated products.

A Tandem Enzymatic sp2 -C-Methylation Process: Coupling in Situ S-Adenosyl-l-Methionine Formation with Methyl Transfer.

A one-pot, two-step biocatalytic platform for the regiospecfic C-methylation and C-ethylation of aromatic substrates is described. The tandem process utilises SalL (Salinospora tropica) for in situ synthesis of S-adenosyl-l-methionine (SAM), followed by alkylation of aromatic substrates by the C-methyltransferase NovO (Streptomyces spheroides). The application of this methodology is demonstrated for the regiospecific labelling of aromatic substrates by the transfer of methyl, ethyl and isotopically labelled 13 CH3,13 CD3 and CD3 groups from their corresponding SAM analogues formed in situ.

Expanding Radical SAM Chemistry by Using Radical Addition Reactions and SAM Analogues.

Radical S-adenosyl-l-methionine (SAM) enzymes utilize a [4Fe-4S] cluster to bind SAM and reductively cleave its carbon-sulfur bond to produce a highly reactive 5'-deoxyadenosyl (dAdo) radical. In almost all cases, the dAdo radical abstracts a hydrogen atom from the substrates or from enzymes, thereby initiating a highly diverse array of reactions. Herein, we report a change of the dAdo radical-based chemistry from hydrogen abstraction to radical addition in the reaction of the radical SAM enzyme NosL. This change was achieved by using a substrate analogue containing an olefin moiety. We also showed that two SAM analogues containing different nucleoside functionalities initiate the radical-based reactions with high efficiencies. The radical adduct with the olefin produced in the reaction was found to undergo two divergent reactions, and the mechanistic insights into this process were investigated in detail. Our study demonstrates a promising strategy in expanding radical SAM chemistry, providing an effective way to access nucleoside-containing compounds by using radical SAM-dependent reactions.

Expanding Radical SAM Chemistry by Using Radical Addition Reactions and SAM Analogues

AbstractRadical S‐adenosyl‐l‐methionine (SAM) enzymes utilize a [4Fe‐4S] cluster to bind SAM and reductively cleave its carbon–sulfur bond to produce a highly reactive 5′‐deoxyadenosyl (dAdo) radical. In almost all cases, the dAdo radical abstracts a hydrogen atom from the substrates or from enzymes, thereby initiating a highly diverse array of reactions. Herein, we report a change of the dAdo radical‐based chemistry from hydrogen abstraction to radical addition in the reaction of the radical SAM enzyme NosL. This change was achieved by using a substrate analogue containing an olefin moiety. We also showed that two SAM analogues containing different nucleoside functionalities initiate the radical‐based reactions with high efficiencies. The radical adduct with the olefin produced in the reaction was found to undergo two divergent reactions, and the mechanistic insights into this process were investigated in detail. Our study demonstrates a promising strategy in expanding radical SAM chemistry, providing an effective way to access nucleoside‐containing compounds by using radical SAM‐dependent reactions.

Abstract 4521: Substrate profiling for SETD8 reveals novel protein targets involved in DNA replication and DNA damage response

Abstract Protein lysine methyltransferases utilize S-adenosyl-L-methionine (SAM) to catalyze the addition of methyl groups to specific lysine residues in both histones and non-histone proteins. Recent evidence indicates that their dysregulation is closely linked to the development and progression of cancer, making them potential therapeutic targets. SETD8 is the sole methyltransferase responsible for mono-methylation of histone H4 lysine 20 (H4K20me1). Its activity is essential for cell viability and has been associated with many essential cellular processes including transcriptional regulation, heterochromatin formation, genomic stability and cell-cycle progression. SETD8 is overexpressed in several types of cancer and may play important roles on malignancy through its trans-methylation activity or by direct interaction with its binding partners. It has been reported that the association between SETD8 and TWIST, a regulator of epithelial-mesenchymal transition, enhances the invasiveness of breast cancer cells. In addition, it was shown that SETD8-mediated methylation of p53 suppresses p53 dependent transcription activation in cancer cells. Despite the identification of a few non-histone proteins such as p53, PCNA and Numb as SETD8's substrates, a comprehensive investigation of new potential substrates is lacking to date. Here we used Bioorthogonal Profiling of Protein Methylation (BPPM) with engineered SETD8 and synthetic SAM analogues to profile novel substrates for SETD8. We identified SETD8 mutants amenable to accommodate non-native SAM analogues containing a terminal alkyne moiety for click chemistry. The engineered SETD8 can transfer this distinct chemical moiety into target proteins for subsequent pulldown and identification of the modified substrates. The BBPM technology applied here revealed previously known substrates of SETD8 as well as novel SETD8 targets. Among the main targets of our interest are those involved in DNA replication and DNA damage response. Our finding is expected to bring new perspectives on the biological importance of SETD8 as well as on its role in carcinogenesis. Citation Format: Fabio Pittella Silva, Gil Blum, Chamara Senevirathne, Minkui Luo. Substrate profiling for SETD8 reveals novel protein targets involved in DNA replication and DNA damage response. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4521.