Substituting N(epsilon)-thioacetyl-lysine for N(epsilon)-acetyl-lysine in peptide substrates as a general approach to inhibiting human NAD(+)-dependent protein deacetylases. Int J Mol Sci. 2008;9:1-11. [PMID: 19325715 PMCID: PMC2635597 DOI: 10.3390/ijms9010001]

Current Trends in Sirtuin Activator and Inhibitor Development

Sirtuins are NAD+-dependent protein deacylases and key metabolic regulators, coupling the cellular energy state with selective lysine deacylation to regulate many downstream cellular processes. Humans encode seven sirtuin isoforms (Sirt1-7) with diverse subcellular localization and deacylase targets. Sirtuins are considered protective anti-aging proteins since increased sirtuin activity is canonically associated with lifespan extension and decreased activity with developing aging-related diseases. However, sirtuins can also assume detrimental cellular roles where increased activity contributes to pathophysiology. Modulation of sirtuin activity by activators and inhibitors thus holds substantial potential for defining the cellular roles of sirtuins in health and disease and developing therapeutics. Instead of being comprehensive, this review discusses the well-characterized sirtuin activators and inhibitors available to date, particularly those with demonstrated selectivity, potency, and cellular activity. This review also provides recommendations regarding the best-in-class sirtuin activators and inhibitors for practical research as sirtuin modulator discovery and refinement evolve.

Biosynthesis of anticancer phytochemical compounds and their chemistry

Cancer is a severe health issue, and cancer cases are rising yearly. New anticancer drugs have been developed as our understanding of the molecular mechanisms behind diverse solid tumors, and metastatic malignancies have increased. Plant-derived phytochemical compounds target different oncogenes, tumor suppressor genes, protein channels, immune cells, protein channels, and pumps, which have attracted much attention for treating cancer in preclinical studies. Despite the anticancer capabilities of these phytochemical compounds, systemic toxicity, medication resistance, and limited absorption remain more significant obstacles in clinical trials. Therefore, drug combinations of new phytochemical compounds, phytonanomedicine, semi-synthetic, and synthetic analogs should be considered to supplement the existing cancer therapies. It is also crucial to consider different strategies for increased production of phytochemical bioactive substances. The primary goal of this review is to highlight several bioactive anticancer phytochemical compounds found in plants, preclinical research, their synthetic and semi-synthetic analogs, and clinical trials. Additionally, biotechnological and metabolic engineering strategies are explored to enhance the production of bioactive phytochemical compounds. Ligands and their interactions with their putative targets are also explored through molecular docking studies. Therefore, emphasis is given to gathering comprehensive data regarding modern biotechnology, metabolic engineering, molecular biology, and in silico tools.

Hydroxamic acid-modified peptide microarrays for profiling isozyme-selective interactions and inhibition of histone deacetylases

Histones control gene expression by regulating chromatin structure and function. The posttranslational modifications (PTMs) on the side chains of histones form the epigenetic landscape, which is tightly controlled by epigenetic modulator enzymes and further recognized by so-called reader domains. Histone microarrays have been widely applied to investigate histone-reader interactions, but not the transient interactions of Zn²⁺-dependent histone deacetylase (HDAC) eraser enzymes. Here, we synthesize hydroxamic acid-modified histone peptides and use them in femtomolar microarrays for the direct capture and detection of the four class I HDAC isozymes. Follow-up functional assays in solution provide insights into their suitability to discover HDAC substrates and inhibitors with nanomolar potency and activity in cellular assays. We conclude that similar hydroxamic acid-modified histone peptide microarrays and libraries could find broad application to identify class I HDAC isozyme-specific substrates and facilitate the development of isozyme-selective HDAC inhibitors and probes.

Side-chain thioamides as fluorescence quenching probes

Thioamides, single atom oxygen-to-sulfur substitutions of canonical amide bonds, can be valuable probes for protein folding and protease studies. Here, we investigate the fluorescence quenching properties of thioamides incorporated into the side-chains of amino acids. We synthesize and incorporate Fmoc-protected, solid-phase peptide synthesis building blocks for introducing Nε -thioacetyl-lysine and γ-thioasparagine. Using rigid model peptides, we demonstrate the distance-dependent fluorescence quenching of these thioamides. Furthermore, we describe attempts to incorporate of Nε -thioacetyl-lysine into proteins expressed in Escherichia coli using amber codon suppression.

One-Atom Substitution Enables Direct and Continuous Monitoring of Histone Deacylase Activity

We developed a one-step direct assay for the determination of histone deacylase (HDAC) activity by substituting the carbonyl oxygen of the acyl moiety with sulfur, resulting in thioacylated lysine side chains. This modification is recognized by class I HDACs with different efficiencies ranging from not accepted for HDAC1 to kinetic constants similar to that of the parent oxo substrate for HDAC8. Class II HDACs can hydrolyze thioacylated substrates with approximately 5-10-fold reduced k_cat values, which resembles the effect of thioamide substitution in metallo-protease substrates. Class IV HDAC11 accepts thiomyristoyl modification less efficiently with an ∼5-fold reduced specificity constant. On the basis of the unique spectroscopic properties of thioamide bonds (strong absorption in spectral range of 260-280 nm and efficient fluorescence quenching), HDAC-mediated cleavage of thioamides could be followed by ultraviolet-visible and fluorescence spectroscopy in a continuous manner. The HDAC activity assay is compatible with microtiter plate-based screening formats up to 1536-well plates with Z' factors of >0.75 and signal-to-noise ratios of >50. Using thioacylated lysine residues in p53-derived peptides, we optimized substrates for HDAC8 with a catalytic efficiency of >250000 M^-1 s^-1, which are more than 100-fold more effective than most of the known substrates. We determined inhibition constants of several inhibitors for human HDACs using thioacylated peptidic substrates and found good correlation with the values from the literature. On the other hand, we could introduce N-methylated, N-acylated lysine residues as inhibitors for HDACs with an IC₅₀ value of 1 μM for an N-methylated, N-myristoylated peptide derivative and human HDAC11.

Autoantibodies as Diagnostic Markers and Mediator of Joint Inflammation in Arthritis

Rheumatoid arthritis is a systemic, polygenic, and multifactorial syndrome characterized by erosive polyarthritis, damage to joint architecture, and presence of autoantibodies against several self-structures in the serum and synovial fluid. These autoantibodies (anticitrullinated protein/peptide antibodies (ACPAs), rheumatoid factors (RF), anticollagen type II antibodies, antiglucose-6 phosphate isomerase antibodies, anticarbamylated protein antibodies, and antiacetylated protein antibodies) have different characteristics, diagnostic/prognostic value, and pathological significance in RA patients. Some of these antibodies are present in the patients' serum several years before the onset of clinical disease. Various genetic and environmental factors are associated with autoantibody production against different autoantigenic targets. Both the activating and inhibitory FcγRs and the activation of different complement cascades contribute to the downstream effector functions in the antibody-mediated disease pathology. Interplay between several molecules (cytokines, chemokines, proteases, and inflammatory mediators) culminates in causing damage to the articular cartilage and bones. In addition, autoantibodies are proven to be useful disease markers for RA, and different diagnostic tools are being developed for early diagnosis of the clinical disease. Recently, a direct link was proposed between the presence of autoantibodies and bone erosion as well as in the induction of pain. In this review, the diagnostic value of autoantibodies, their synthesis and function as a mediator of joint inflammation, and the significance of IgG-Fc glycosylation are discussed.

Sirtuin activators and inhibitors: Promises, achievements, and challenges

The NAD⁺-dependent protein lysine deacylases of the Sirtuin family regulate various physiological functions, from energy metabolism to stress responses. The human Sirtuin isoforms, SIRT1-7, are considered attractive therapeutic targets for aging-related diseases, such as type 2 diabetes, inflammatory diseases and neurodegenerative disorders. We review the status of Sirtuin-targeted drug discovery and development. Potent and selective pharmacological Sirt1 activators and inhibitors are available, and initial clinical trials have been carried out. Several promising inhibitors and activators have also been described for other isoforms. Progress in understanding the mechanisms of Sirtuin modulation by such compounds provides a rational basis for further drug development.

Targeting Sirtuins: Substrate Specificity and Inhibitor Design

Lysine residues across the proteome are modified by posttranslational modifications (PTMs) that significantly enhance the structural and functional diversity of proteins. For lysine, the most abundant PTM is ɛ-N-acetyllysine (Kac), which plays numerous roles in regulation of important cellular functions, such as gene expression (epigenetic effects) and metabolism. A family of enzymes, namely histone deacetylases (HDACs), removes these PTMs. A subset of these enzymes, the sirtuins (SIRTs), represent class III HDAC and, unlike the rest of the family, these hydrolases are NAD⁺-dependent. Although initially described as deacetylases, alternative deacylase functions for sirtuins have been reported, which expands the potential cellular roles of this class of enzymes. Currently, sirtuins are investigated as therapeutic targets for the treatment of diseases that span from cancers to neurodegenerative disorders. In the present book chapter, we review and discuss the current literature on novel ɛ-N-acyllysine PTMs, targeted by sirtuins, as well as mechanism-based sirtuin inhibitors inspired by their substrates.

Genetically encoding thioacetyl-lysine as a non-deacetylatable analog of lysine acetylation in Escherichia coli

Reversible lysine acetylation is one of the most widely distributed post-translational modifications; it is involved in a variety of biological processes and can be found in all three domains of life. Acetyltransferases and deacetylases work coordinately to control levels of protein acetylation. In this work, we applied the genetic code expansion strategy to site-specifically incorporate Nε-thioacetyl-l-lysine (TAcK) as an analog of Nε-acetyl-l-lysine (AcK) into green fluorescent protein and malate dehydrogenase in Escherichia coli. We showed that TAcK could serve as an ideal functional mimic for AcK. It could also resist the bacterial sirtuin-type deacetylase CobB. Thus, genetic incorporation of TAcK as a non-deacetylatable analog of AcK into proteins will facilitate in vivo studies of protein acetylation.

The Current State of NAD+ -Dependent Histone Deacetylases (Sirtuins) as Novel Therapeutic Targets

Sirtuins are NAD⁺ -dependent protein deacylases that cleave off acetyl, as well as other acyl groups, from the ε-amino group of lysines in histones and other substrate proteins. Seven sirtuin isotypes (Sirt1-7) have been identified in mammalian cells. As sirtuins are involved in the regulation of various physiological processes such as cell survival, cell cycle progression, apoptosis, DNA repair, cell metabolism, and caloric restriction, a dysregulation of their enzymatic activity has been associated with the pathogenesis of neoplastic, metabolic, infectious, and neurodegenerative diseases. Thus, sirtuins are promising targets for pharmaceutical intervention. Growing interest in a modulation of sirtuin activity has prompted the discovery of several small molecules, able to inhibit or activate certain sirtuin isotypes. Herein, we give an update to our previous review on the topic in this journal (Schemies, 2010), focusing on recent developments in sirtuin biology, sirtuin modulators, and their potential as novel therapeutic agents.

Using mitochondrial sirtuins as drug targets: disease implications and available compounds

Sirtuins are an evolutionary conserved family of NAD(+)-dependent protein lysine deacylases. Mammals have seven Sirtuin isoforms, Sirt1-7. They contribute to regulation of metabolism, stress responses, and aging processes, and are considered therapeutic targets for metabolic and aging-related diseases. While initial studies were focused on Sirt1 and 2, recent progress on the mitochondrial Sirtuins Sirt3, 4, and 5 has stimulated research and drug development for these isoforms. Here we review the roles of Sirtuins in regulating mitochondrial functions, with a focus on the mitochondrially located isoforms, and on their contributions to disease pathologies. We further summarize the compounds available for modulating the activity of these Sirtuins, again with a focus on mitochondrial isoforms, and we describe recent results important for the further improvement of compounds. This overview illustrates the potential of mitochondrial Sirtuins as drug targets and summarizes the status, progress, and challenges in developing small molecule compounds modulating their activity.

Sirtuin functions and modulation: from chemistry to the clinic

Sirtuins are NAD(+)-dependent histone deacetylases regulating important metabolic pathways in prokaryotes and eukaryotes and are involved in many biological processes such as cell survival, senescence, proliferation, apoptosis, DNA repair, cell metabolism, and caloric restriction. The seven members of this family of enzymes are considered potential targets for the treatment of human pathologies including neurodegenerative diseases, cardiovascular diseases, and cancer. Furthermore, recent interest focusing on sirtuin modulators as epigenetic players in the regulation of fundamental biological pathways has prompted increased efforts to discover new small molecules able to modify sirtuin activity. Here, we review the role, mechanism of action, and biological function of the seven sirtuins, as well as their inhibitors and activators.

A continuous sirtuin activity assay without any coupling to enzymatic or chemical reactions

Sirtuins are NAD(+) dependent lysine deacylases involved in many regulatory processes such as control of metabolic pathways, DNA repair and stress response. Modulators of sirtuin activity are required as tools for uncovering the biological function of these enzymes and as potential therapeutic agents. Systematic discovery of such modulators is hampered by the lack of direct and continuous activity assays. The present study describes a novel continuous assay based on the increase of a fluorescence signal subsequent to sirtuin mediated removal of a fluorescent acyl chain from a modified TNFα-derived peptide. This substrate is well recognized by human sirtuins 1-6 and represents the best sirtuin 2 substrate described so far with a kcat/KM-value of 176 000 M(-1)s(-1). These extraordinary substrate properties allow the first determination of Ki-values for the specific Sirt2 inhibitory peptide S2iL5 (600 nM) and for the quasi-universal sirtuin inhibitor peptide thioxo myristoyl TNFα (80 nM).

Human SIRT3 tripeptidic inhibitors containing N(ε)-thioacetyl-lysine

Built upon our lead pan-SIRT1/2/3 tripeptidic inhibitors that contain the catalytic mechanism-based sirtuin inhibitory warhead N(ε)-thioacetyl-lysine, three of their analogs (i.e., 7, 9, and 19) were discovered in the current study to exhibit a significantly enhanced SIRT3 inhibitory selectivity while maintaining the SIRT3 inhibitory potency. These compounds represent novel lead compounds for developing more potent and selective SIRT3 inhibitors of the catalytic mechanism-based type.

Targeting chromatin to improve radiation response

Chromatin, the structure formed by the wrapping of approximately 146 base pairs of DNA around an octamer of histones, has a profound impact on numerous DNA-based processes. Chromatin modifications and chromatin remodellers have recently been implicated in important aspects of the DNA damage response including facilitating the initial sensing of the damage as well as subsequent recruitment of repair factors. Radiation is an effective cancer therapy for a large number of tumours, and there is considerable interest in finding approaches that might further increase the efficacy of radiotherapy. The use of radiation leads to the generation of DNA damage and, therefore, agents that can affect the sensing and repair of DNA damage may have an impact on overall radiation efficacy. The chromatin modifications as well as chromatin modifiers that have been associated with the DNA damage response will be summarized in this review. An emphasis will be placed on those processes that can be pharmacologically manipulated with currently available inhibitors. The rationale for the use of these inhibitors in combination with radiation will also be described.

Epigenetic dysregulation in Epstein-Barr virus-associated gastric carcinoma: Disease and treatments

Epstein-Barr virus (EBV)-associated gastric carcinoma (EBVaGC) comprises nearly 10% of gastric carcinoma cases worldwide. Recently, it was recognised to have unique clinicopathologic characteristics, including male predominance, lower rates of lymph node involvement, and better prognosis. EBVaGC is further characterised by abnormal hypermethylation of tumour suppressor gene promoter regions, causing down-regulation of their expression. In the present review, we critically discuss the role of EBV in gastric carcinogenesis, summarising the role of viral proteins and microRNAs with respect to aberrant methylation in EBVaGC. Given the role of epigenetic dysregulation in tumourigenesis, epigenetic modifiers may represent a novel therapeutic strategy.

The promise and failures of epigenetic therapies for cancer treatment

Genetic mutations and gross structural defects in the DNA sequence permanently alter genetic loci in ways that significantly disrupt gene function. In sharp contrast, genes modified by aberrant epigenetic modifications remain structurally intact and are subject to partial or complete reversal of modifications that restore the original (i.e. non-diseased) state. Such reversibility makes epigenetic modifications ideal targets for therapeutic intervention. The epigenome of cancer cells is extensively modified by specific hypermethylation of the promoters of tumor suppressor genes relative to the extensive hypomethylation of repetitive sequences, overall loss of acetylation, and loss of repressive marks at microsatellite/repeat regions. In this review, we discuss emerging therapies targeting specific epigenetic modifications or epigenetic modifying enzymes either alone or in combination with other treatment regimens. The limitations posed by cancer treatments elicit unintended epigenetic modifications that result in exacerbation of tumor progression are also discussed. Lastly, a brief discussion of the specificity restrictions posed by epigenetic therapies and ways to address such limitations is presented.

Peptides and Pseudopeptides as SIRT6 Deacetylation Inhibitors

SIRT6 belongs to the family of histone deacetylases (class III), but it also has mono-ADP-ribosyltransferase activity. SIRT6 is a nuclear sirtuin that has been associated with aging, cellular protection, and sugar metabolism. Despite these important roles for SIRT6, thus far, there are only a few weak SIRT6 inhibitors available, and no structure-activity relationship (SAR) studies have been published. This is the first study concerning peptides and pseudopeptides as SIRT6 deacetylation inhibitors and the first SAR data concerning SIRT6. We also investigated the molecular interactions using a homology model. We report three compounds exhibiting 62-91% SIRT6 inhibition at 200 μM concentration. These compounds can serve as starting points for systematic SAR studies and SIRT6 inhibitor design.

Sirtuins: NAD(+)-dependent deacetylase mechanism and regulation

Sirtuins are NAD(+)-dependent deacetylases involved in chemical reversal of acetyllysine modifications of cellular proteins. Deacetylation catalyzed by sirtuins is implicated in regulating diverse biological processes, including energy homeostasis. The mechanism of NAD(+)-dependent deacetylation is proposed to occur via an ADPR-peptidyl-imidate intermediate, resulting from reaction of NAD(+) and an acetyllysine residue. This mechanism enables sirtuins to respond dynamically to intracellular fluctuations of NAD(+) and nicotinamide. Chemical probes such as nicotinamide antagonists and thioacetyl compounds provide key support for the imidate mechanism of sirtuin deacetylation catalysis. Novel new directions include chemical probes to study sirtuins in cells, and the discovery of novel post-translational modifications besides acetyl, such as succinyl and malonyl, that are regulated by sirtuins.

Structure-based design of pseudopeptidic inhibitors for SIRT1 and SIRT2

The lack of substrate-bound crystal structures of SIRT1 and SIRT2 complicates the drug design for these targets. In this work, we aim to study whether SIRT3 could serve as a target structure in the design of substrate based pseudopeptidic inhibitors of SIRT1 and SIRT2. We created a binding hypothesis for pseudopeptidic inhibitors, synthesized a series of inhibitors, and studied how well the fulfillment of the binding criteria proposed by the hypothesis correlated with the in vitro inhibitory activities. The chosen approach was further validated by studying docking results between 12 different SIRT3, Sir2Tm, SIRT1 and SIRT2 X-ray structures and homology models in different conformational forms. It was concluded that the created binding hypothesis can be used in the design of the substrate based inhibitors of SIRT1 and SIRT2 although there are some reservations, and it is better to use the substrate-bound structure of SIRT3 instead of the available apo-SIRT2 as the target structure.

A mechanism-based potent sirtuin inhibitor containing Nε-thiocarbamoyl-lysine (TuAcK)

In the current study, we have identified N(ε)-thiocarbamoyl-lysine (TuAcK) as a general sirtuin inhibitory warhead which was shown to be able to confer potent sirtuin inhibition. This inhibition was also shown to be mechanism-based in that the TuAck residue was able to be processed by a sirtuin enzyme with the formation of a stalled S-alkylamidate intermediate.

NAD(+) -dependent histone deacetylases (sirtuins) as novel therapeutic targets

Histone deacetylases (HDACs) are enzymes that cleave off acetyl groups from acetyl-lysine residues in histones and various nonhistone proteins. Four different classes of HDACs have been identified in humans so far. Although classes I, II, and IV are zinc-dependent amidohydrolases, class III HDACs depend on nicotinamide adenine dinucleotide (NAD(+)) for their catalytic activity. According to their homology to Sir2p, a yeast histone deacetylase, the class III is also termed sirtuins. Seven members have been described in humans so far. As sirtuins are involved in many physiological and pathological processes, their activity has been associated with the pathogenesis of cancer, HIV, metabolic, or neurological diseases. Herein, we present an overview over sirtuins including their biology, targets, inhibitors, and activators and their potential as new therapeutic agents.

Mechanism-based affinity capture of sirtuins

The ability to probe for catalytic activities of enzymes and to detect their abundance in complex biochemical contexts has traditionally relied on a combination of kinetic assays and techniques such as western blots that use expensive reagents such as antibodies. The ability to simultaneously detect activity and isolate a protein catalyst from a mixture is even more difficult and currently impossible in most cases. In this manuscript we describe a chemical approach that achieves this goal for a unique family of enzymes called sirtuins using novel chemical tools, enabling rapid detection of activity and isolation of these protein catalysts. Sirtuin deacetylases are implicated in the regulation of many physiological functions including energy metabolism, DNA-damage response, and cellular stress resistance. We synthesized an aminooxy-derivatized NAD(+) and a pan-sirtuin inhibitor that reacts on sirtuin active sites to form a chemically stable complex that can subsequently be crosslinked to an aldehyde-substituted biotin. Subsequent retrieval of the biotinylated sirtuin complexes on streptavidin beads followed by gel electrophoresis enabled simultaneous detection of active sirtuins, isolation and molecular weight determination. We show that these tools are cross reactive against a variety of human sirtuin isoforms including SIRT1, SIRT2, SIRT3, SIRT5, SIRT6 and can react with microbial derived sirtuins as well. Finally, we demonstrate the ability to simultaneously detect multiple sirtuin isoforms in reaction mixtures with this methodology, establishing proof of concept tools for chemical studies of sirtuins in complex biological samples.

Sirtuin mechanism and inhibition: explored with N(ε)-acetyl-lysine analogs

Silent information regulator 2 (Sir2) enzymes or sirtuins are a family of intracellular protein deacetylases that can catalyze the β-nicotinamide adenine dinucleotide (β-NAD(+))-dependent deacetylation of N(ε)-acetyl-lysine on protein substrates, with the formation of lysine N(ε)-deacetylated protein species and small molecule products, i.e. nicotinamide and 2'-O-acetyl-ADP-ribose (2'-O-AADPR). These enzymes are evolutionarily conserved among all the three kingdoms of life, with the yeast Sir2 being the founding family member. In humans, seven sirtuins, i.e. SIRT1-7, have been identified. The past a few years have witnessed a tremendous interest in investigating the unique mechanism for the sirtuin-catalyzed deacetylation reaction. We have also seen a lot of research employing different strategies to identify different types of the inhibitors for this enzymatic deacetylation reaction. These inhibitors hold great potential toward a fuller exploration of sirtuin biology and pharmacology as well as toward developing novel therapeutics for metabolic and age-related diseases and cancer. Here we would like to review the significant contributions that the judicious use of a variety of N(ε)-acetyl-lysine analogs has been able to make toward our enhanced mechanistic understanding and capability of pharmacological exploitation of the sirtuin-catalyzed deacetylation reaction.

Inhibitors to understand molecular mechanisms of NAD(+)-dependent deacetylases (sirtuins)

Histone deacetylases (HDACs) are enzymes that cleave acetyl groups from acetyl-lysine residues in histones and various nonhistone proteins. Unlike the other three of the four classes of HDACs that have been identified in humans, which are zinc-dependent amidohydrolases, class III HDACs depend on nicotinamide adenine dinucleotide (NAD(+)) for their catalytic activity. The seven members of the class III HDACs are also named sirtuins for their homology to Sir2p, a yeast histone deacetylase. Sirtuin inhibitors have been critical for the linkage of sirtuin activity to many physiological and pathological processes, and sirtuin activity has been associated with the pathogenesis of cancer, HIV, and metabolic and neurological diseases. Presented here is an overview of the many sirtuin inhibitors that have provided insight into the biological role of sirtuins.

N(epsilon)-Modified lysine containing inhibitors for SIRT1 and SIRT2

Sirtuins catalyze the NAD(+) dependent deacetylation of N(epsilon)-acetyl lysine residues to nicotinamide, O'-acetyl-ADP-ribose (OAADPR) and N(epsilon)-deacetylated lysine. Here, an easy-to-synthesize Ac-Ala-Lys-Ala sequence has been used as a probe for the screening of novel N(epsilon)-modified lysine containing inhibitors against SIRT1 and SIRT2. N(epsilon)-Selenoacetyl and N(epsilon)-isothiovaleryl were the most potent moieties found in this study, comparable to the widely studied N(epsilon)-thioacetyl group. The N(epsilon)-3,3-dimethylacryl and N(epsilon)-isovaleryl moieties gave significant inhibition in comparison to the N(epsilon)-acetyl group present in the substrates. In addition, the studied N(epsilon)-alkanoyl, N(epsilon)-alpha,beta-unsaturated carbonyl and N(epsilon)-aroyl moieties showed that the acetyl binding pocket can accept rather large groups, but is sensitive to even small changes in electronic and steric properties of the N(epsilon)-modification. These results are applicable for further screening of N(epsilon)-acetyl analogues.

Substrate specificity of SIRT1-catalyzed lysine Nepsilon-deacetylation reaction probed with the side chain modified Nepsilon-acetyl-lysine analogs

Peptides containing L-N(epsilon)-acetyl-lysine (L-AcK) or its side chain modified analogs were prepared and assayed using SIRT1, the prototypical human silent information regulator 2 (Sir2) enzyme. While previous studies showed that the side chain acetyl group of L-AcK can be extended to bulkier acyl groups for Sir2 (including SIRT1)-catalyzed lysine N(epsilon)-deacylation reaction, our current study suggested that SIRT1-catalyzed deacetylation reaction had a very stringent requirement for the distance between the alpha-carbon and the side chain acetamido group, with that found in L-AcK being optimal. Moreover, our current study showed that SIRT1 catalyzed the stereospecific deacetylation of L-AcK versus its D-isomer. The results from our current study shall constitute another piece of important information to be considered when designing inhibitors for SIRT1 and Sir2 enzymes in general.

N(epsilon)-thioacetyl-lysine-containing tri-, tetra-, and pentapeptides as SIRT1 and SIRT2 inhibitors

N()-Thioacetyl-lysine-containing tri-, tetra-, and pentapeptides, based on the alpha-tubulin and p53 protein sequences, were studied as SIRT1 and SIRT2 inhibitors. The potency of the pentapeptides depended on the selection of the side chains. The removal of N- and C-terminal residues of the pentapeptides yielded tripeptides with retained SIRT1 inhibitory activity but decreased SIRT2 inhibitory activity. The most potent SIRT1 inhibitors were equipotent with the reference compound (6-chloro-2,3,4,9-tetrahydro-1H-carbazole-1-carboxamide) with the IC(50) values of 180-330 nM.

Mechanisms and molecular probes of sirtuins

Sirtuins are critical regulators of many cellular processes, including insulin secretion, the cell cycle, and apoptosis. Sirtuins are associated with a variety of age-associated diseases such as type II diabetes, obesity, and Alzheimer's disease. A thorough understanding of sirtuin chemical mechanisms will aid toward developing novel therapeutics that regulate metabolic disorders and combat associated diseases. In this review, we discuss the unique deacetylase mechanism of sirtuins and how this information might be employed to develop inhibitors and other molecular probes for therapeutic and basic research applications. We also cover physiological regulation of sirtuin activity and how these modes of regulation may be exploited to manipulate sirtuin activity in live cells. Development of molecular probes and drugs that specifically target sirtuins will further understanding of sirtuin biology and potentially afford new treatments of several human diseases.