N-myristoyltransferase

Phytochemical Composition and Pharmacological Activities of Three Essential Oils Collected from Eastern Morocco (Origanum compactum, Salvia officinalis, and Syzygium aromaticum): A Comparative Study

Throughout history, essential oils have been employed for their pleasing scents and potential therapeutic benefits. These oils have shown promise in various areas, including aromatherapy, personal care products, natural remedies, and even as alternatives to traditional cleaning agents or pest control solutions. The study aimed to explore the chemical makeup, antioxidant, and antibacterial properties of Origanum compactum Benth., Salvia officinalis L., and Syzygium aromaticum (L.) Merr. et Perry. Initially, the composition of the three essential oils, O. compactum (HO), S. officinalis (HS), and S. aromaticum (HC) was analyzed using GC-MS technology, revealing significant differences in the identified compounds. α-thujone emerged as the predominant volatile component in the oils, making up 78.04% of the composition, followed by eugenol, which constituted 72.66% and 11.22% of the HC and HO oils, respectively. To gauge antioxidant capabilities, tests involving DPPH scavenging capacity and total antioxidant capacity were conducted. Antioxidant activity was determined through the phosphomolybdate test and the DPPH• radical scavenging activity, with the HO essential oil displaying significant scavenging capacity (IC50 of 0.12 ± 0.02 mg/mL), similar to ascorbic acid (IC50 of 0.26 ± 0.24 mg/mL). Similarly, the TAC assay for HO oil revealed an IC50 of 1086.81 ± 0.32 µM AAE/mg. Additionally, the oils' effectiveness against four bacterial strains, namely Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Listeria monocytogenes, and five fungi, Geotrichum candidum, Aspergillus niger, Saccharomyces cerevisiae, Candida glabrata, and Candida albicans, was tested in vitro. The examined essential oils generally exhibited limited antimicrobial effects, with the exception of HC oil, which demonstrated an exceptionally impressive level of antifungal activity. In order to clarify the antioxidant, antibacterial, and antifungal effects of the identified plant compounds, we employed computational methods, specifically molecular docking. This technique involved studying the interactions between these compounds and established protein targets associated with antioxidant, antibacterial, and antifungal activities.

Pharmacological Properties of Chemically Characterized Extracts from Mastic Tree: In Vitro and In Silico Assays

The mastic tree, scientifically known as Pistacia lentiscus, which belongs to the Anacardiaceae family, was used in this study. The aim of this research was to analyze the chemical composition of this plant and assess its antioxidant and antibacterial properties using both laboratory experiments and computer simulations through molecular docking, a method that predicts the binding strength of a small molecule to a protein. The soxhlet method (SE) was employed to extract substances from the leaves of P. lentiscus found in the eastern region of Morocco. Hexane and methanol were the solvents used for the extraction process. The n-hexane extract was subjected to gas chromatography-mass spectrometry (GC/MS) to identify its fatty acid content. The methanolic extract underwent high-performance liquid chromatography with a diode-array detector (HPLC-DAD) to determine the presence of phenolic compounds. Antioxidant activity was assessed using the DPPH spectrophotometric test. The findings revealed that the main components in the n-hexane extract were linoleic acid (40.97 ± 0.33%), oleic acid (23.69 ± 0.12%), and palmitic acid (22.83 ± 0.10%). Catechin (37.05 ± 0.15%) was identified as the predominant compound in the methanolic extract through HPLC analysis. The methanolic extract exhibited significant DPPH radical scavenging, with an IC50 value of 0.26 ± 0.14 mg/mL. The antibacterial activity was tested against Staphylococcus aureus, Listeria innocua, and Escherichia coli, while the antifungal activity was evaluated against Geotrichum candidum and Rhodotorula glutinis. The P. lentiscus extract demonstrated notable antimicrobial effects. Additionally, apart from molecular docking, other important factors, such as drug similarity, drug metabolism and distribution within the body, potential adverse effects, and impact on bodily systems, were considered for the substances derived from P. lentiscus. Scientific algorithms, such as Prediction of Activity Spectra for Substances (PASS), Absorption, Distribution, Metabolism, Excretion (ADME), and Pro-Tox II, were utilized for this assessment. The results obtained from this research support the traditional medicinal usage of P. lentiscus and suggest its potential for drug development.

Exploring N-myristoyltransferase as a promising drug target against parasitic neglected tropical diseases

Neglected tropical diseases (NTDs) constitute a group of approximately 20 infectious diseases that mainly affect the impoverished population without basic sanitation in tropical countries. These diseases are responsible for many deaths worldwide, costing billions of dollars in public health investment to treat and control these infections. Among them are the diseases caused by protozoa of the Trypanosomatid family, which constitute Trypanosoma cruzi (Chagas disease), Trypanosoma brucei (sleeping sickness), and Leishmaniasis. In addition, there is a classification of other diseases, called the big three, AIDS, tuberculosis, and malaria, which are endemic in countries with tropical conditions. Despite the high mortality rates, there is still a gap in the treatment. The drugs have a high incidence of side effects and protozoan resistance, justifying the investment in developing new alternatives. In fact, the Target-Based Drug Design (TBDD) approach is responsible for identifying several promising compounds, and among the targets explored through this approach, N-myristoyltransferase (NMT) stands out. It is an enzyme related to the co-translational myristoylation of N-terminal glycine in various peptides. The myristoylation process is a co-translation that occurs after removing the initiator methionine. This process regulates the assembly of protein complexes and stability, which justifies its potential as a drug target. In order to propose NMT as a potential target for parasitic diseases, this review will address the entire structure and function of this enzyme and the primary studies demonstrating its promising potential against Leishmaniasis, T. cruzi, T. brucei, and malaria. We hope our information can help researchers worldwide search for potential drugs against these diseases that have been threatening the health of the world's population.

Assessment of the Antioxidant and Antimicrobial Potential of Ptychotis verticillata Duby Essential Oil from Eastern Morocco: An In Vitro and In Silico Analysis

Ptychotis verticillata Duby, referred to as Nûnkha in the local language, is a medicinal plant that is native to Morocco. This particular plant is a member of the Apiaceae family and has a longstanding history in traditional medicine and has been utilized for therapeutic purposes by practitioners for generations. The goal of this research is to uncover the phytochemical makeup of the essential oil extracted from P. verticillata, which is indigenous to the Touissite region in Eastern Morocco. The extraction of the essential oil of P. verticillata (PVEO) was accomplished through the use of hydro-distillation via a Clevenger apparatus. The chemical profile of the essential oil was then determined through analysis utilizing gas chromatography–mass spectrometry (GC/MS). The study findings indicated that the essential oil of P. verticillata is composed primarily of Carvacrol (37.05%), D-Limonene (22.97%), γ-Terpinene (15.97%), m-Cymene (12.14%) and Thymol (8.49%). The in vitro antioxidant potential of PVEO was evaluated using two methods: the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical trapping assay and the ferric reducing antioxidant power (FRAP) method. The data demonstrated considerable radical scavenging and relative antioxidative power. Escherichia coli, Staphylococcus aureus, Listeria innocua, and Pseudomonas aeruginosa were the most susceptible bacterial strains tested, while Geotrichum candidum, Candida albicans, and Rhodotorula glutinis were the most resilient fungi strains. PVEO had broad-spectrum antifungal and antibacterial properties. To elucidate the antioxidative and antibacterial characteristics of the identified molecules, we applied the methodology of molecular docking, a computational approach that forecasts the binding of a small molecule to a protein. Additionally, we utilized the Prediction of Activity Spectra for Substances (PASS) algorithm; Absorption, Distribution, Metabolism, and Excretion (ADME); and Pro-Tox II (to predict the toxicity in silico) tests to demonstrate PVEO’s identified compounds’ drug-likeness, pharmacokinetic properties, the anticipated safety features after ingestion, and the potential pharmacological activity. Finally, our findings scientifically confirm the ethnomedicinal usage and usefulness of this plant, which may be a promising source for future pharmaceutical development.

Localized Proteasomal Degradation: From the Nucleus to Cell Periphery

The proteasome is responsible for selective degradation of most cellular proteins. Abundantly present in the cell, proteasomes not only diffuse in the cytoplasm and the nucleus but also associate with the chromatin, cytoskeleton, various membranes and membraneless organelles/condensates. How and why the proteasome gets to these specific subcellular compartments remains poorly understood, although increasing evidence supports the hypothesis that intracellular localization may have profound impacts on the activity, substrate accessibility and stability/integrity of the proteasome. In this short review, I summarize recent advances on the functions, regulations and targeting mechanisms of proteasomes, especially those localized to the nuclear condensates and membrane structures of the cell, and I discuss the biological significance thereof in mediating compartmentalized protein degradation.

Nutrient-Dependent Changes of Protein Palmitoylation: Impact on Nuclear Enzymes and Regulation of Gene Expression

Diet is the main environmental stimulus chronically impinging on the organism throughout the entire life. Nutrients impact cells via a plethora of mechanisms including the regulation of both protein post-translational modifications and gene expression. Palmitoylation is the most-studied protein lipidation, which consists of the attachment of a molecule of palmitic acid to residues of proteins. S-palmitoylation is a reversible cysteine modification finely regulated by palmitoyl-transferases and acyl-thioesterases that is involved in the regulation of protein trafficking and activity. Recently, several studies have demonstrated that diet-dependent molecules such as insulin and fatty acids may affect protein palmitoylation. Here, we examine the role of protein palmitoylation on the regulation of gene expression focusing on the impact of this modification on the activity of chromatin remodeler enzymes, transcription factors, and nuclear proteins. We also discuss how this physiological phenomenon may represent a pivotal mechanism underlying the impact of diet and nutrient-dependent signals on human diseases.

Bm-iAANAT and its potential role in fatty acid amide biosynthesis in Bombyx mori

The purpose of this research is to unravel the substrate specificity and kinetic properties of an insect arylalkylamine N-acyltransferase from Bombyx mori (Bm-iAANAT) and to determine if this enzyme will catalyze the formation of long chain N-acylarylalkylamides in vitro. However, the determination of substrates and products for Bm-iAANAT in vitro is no guarantee that these same molecules are substrates and products for the enzyme in the organism. Therefore, RT-PCR was performed to detect the Bm-iAANAT transcripts and liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) analysis was performed on purified lipid extracts from B. mori larvae (fourth instar, Bmi4) to determine if long chain fatty acid amides are produced in B. mori. Ultimately, we found that recombinant Bm-iAANAT will utilize long-chain acyl-CoA thioesters as substrates and identified Bm-iAANAT transcripts and long-chain fatty acid amides in Bmi4. Together, these data show Bm-iAANAT will catalyze the formation of long-chain N-acylarylalkylamides in vitro and provide evidence demonstrating that Bm-iAANAT has a role in fatty acid amide biosynthesis in B. mori, as well.

Activation of oncogenic tyrosine kinase signaling promotes insulin receptor-mediated cone photoreceptor survival

In humans, daylight vision is primarily mediated by cone photoreceptors. These cells die in age-related retinal degenerations. Prolonging the life of cones for even one decade would have an enormous beneficial effect on usable vision in an aging population. Photoreceptors are postmitotic, but shed 10% of their outer segments daily, and must synthesize the membrane and protein equivalent of a proliferating cell each day. Although activation of oncogenic tyrosine kinase and inhibition of tyrosine phosphatase signaling is known to be essential for tumor progression, the cellular regulation of this signaling in postmitotic photoreceptor cells has not been studied. In the present study, we report that a novel G-protein coupled receptor–mediated insulin receptor (IR) signaling pathway is regulated by non-receptor tyrosine kinase Src through the inhibition of protein tyrosine phosphatase IB (PTP1B). We demonstrated the functional significance of this pathway through conditional deletion of IR and PTP1B in cones, in addition to delaying the death of cones in a mouse model of cone degeneration by activating the Src. This is the first study demonstrating the molecular mechanism of a novel signaling pathway in photoreceptor cells, which provides a window of opportunity to save the dying cones in retinal degenerative diseases.

Myristoylation: An Important Protein Modification in the Immune Response

Protein N-myristoylation is a cotranslational lipidic modification specific to the alpha-amino group of an N-terminal glycine residue of many eukaryotic and viral proteins. The ubiquitous eukaryotic enzyme, N-myristoyltransferase, catalyzes the myristoylation process. Precisely, attachment of a myristoyl group increases specific protein–protein interactions leading to subcellular localization of myristoylated proteins with its signaling partners. The birth of the field of myristoylation, a little over three decades ago, has led to the understanding of the significance of protein myristoylation in regulating cellular signaling pathways in several biological processes especially in carcinogenesis and more recently immune function. This review discusses myristoylation as a prerequisite step in initiating many immune cell signaling cascades. In particular, we discuss the hitherto unappreciated implication of myristoylation during myelopoiesis, innate immune response, lymphopoiesis for T cells, and the formation of the immunological synapse. Furthermore, we discuss the role of myristoylation in inducing the virological synapse during human immunodeficiency virus infection as well as its clinical implication. This review aims to summarize existing knowledge in the field and to highlight gaps in our understanding of the role of myristoylation in immune function so as to further investigate into the dynamics of myristoylation-dependent immune regulation.

How to gather useful and valuable information from protein binding measurements using Langmuir lipid monolayers

This review presents data on the influence of various experimental parameters on the binding of proteins onto Langmuir lipid monolayers. The users of the Langmuir methodology are often unaware of the importance of choosing appropriate experimental conditions to validate the data acquired with this method. The protein Retinitis pigmentosa 2 (RP2) has been used throughout this review to illustrate the influence of these experimental parameters on the data gathered with Langmuir monolayers. The methods detailed in this review include the determination of protein binding parameters from the measurement of adsorption isotherms, infrared spectra of the protein in solution and in monolayers, ellipsometric isotherms and fluorescence micrographs.

N-terminal protein modifications: Bringing back into play the ribosome

N-terminal protein modifications correspond to the first modifications which in principle any protein may undergo, before translation is completed by the ribosome. This class of essential modifications can have different nature or function and be catalyzed by a variety of dedicated enzymes. Here, we review the current state of the major N-terminal co-translational modifications, with a particular emphasis to their catalysts, which belong to metalloprotease and acyltransferase clans. The earliest of these modifications corresponds to the N-terminal methionine excision, an ubiquitous and essential process leading to the removal of the first methionine. N-alpha acetylation occurs also in all Kingdoms although its extent appears to be significantly increased in higher eukaryotes. Finally, N-myristoylation is a crucial pathway existing only in eukaryotes. Recent studies dealing on how some of these co-translational modifiers might work in close vicinity of the ribosome is starting to provide new information on when these modifications exactly take place on the elongating nascent chain and the interplay with other ribosome biogenesis factors taking in charge the nascent chains. Here a comprehensive overview of the recent advances in the field of N-terminal protein modifications is given.

The myristoylated amino-terminus of an Arabidopsis calcium-dependent protein kinase mediates plasma membrane localization

Calcium-dependent protein kinases (CDPK) are a major group of calcium-stimulated kinases found in plants and some protists. Many CDPKs are membrane-associated, presumably because of lipid modifications at their amino termini. We investigated the subcellular location and myristoylation of AtCPK5, a member of the Arabidopsis CDPK family. Most AtCPK5 was associated with the plasma membrane as demonstrated by two-phase fractionation of plant microsomes and by in vivo detection of AtCPK5-GFP fusion proteins. AtCPK5 was a substrate for plant N-myristoyltransferase and myristoylation was prevented by converting the glycine at the proposed site of myristate attachment to alanine (G2A). In transgenic plants, a G2A mutation completely abolished AtCPK5 membrane association, indicating that myristoylation was essential for membrane binding. The first sixteen amino acids of AtCPK5 were sufficient to direct plasma membrane localization. In addition, differentially phosphorylated forms of AtCPK5 were detected both in planta and after expression of AtCPK5 in a cell-free plant extract. Our results demonstrate that AtCPK5 is myristoylated at its amino terminus and that myristoylation is required for membrane binding.

Golgi traffic and integrity depend on N-myristoyl transferase-1 in Arabidopsis

N-myristoylation is a crucial irreversible eukaryotic lipid modification allowing a key subset of proteins to be targeted at the periphery of specific membrane compartments. Eukaryotes have conserved N-myristoylation enzymes, involving one or two N-myristoyltransferases (NMT1 and NMT2), among which NMT1 is the major enzyme. In the postembryonic developmental stages, defects in NMT1 lead to aberrant cell polarity, flower differentiation, fruit maturation, and innate immunity; however, no specific NMT1 target responsible for such deficiencies has hitherto been identified. Using a confocal microscopy forward genetics screen for the identification of Arabidopsis thaliana secretory mutants, we isolated STINGY, a recessive mutant with defective Golgi traffic and integrity. We mapped STINGY to a substitution at position 160 of Arabidopsis NMT1 (NMT1A160T). In vitro kinetic studies with purified NMT1A160T enzyme revealed a significant reduction in its activity due to a remarkable decrease in affinity for both myristoyl-CoA and peptide substrates. We show here that this recessive mutation is responsible for the alteration of Golgi traffic and integrity by predominantly affecting the Golgi membrane/cytosol partitioning of ADP-ribosylation factor proteins. Our results provide important functional insight into N-myristoylation in plants by ascribing postembryonic functions of Arabidopsis NMT1 that involve regulation of the functional and morphological integrity of the plant endomembranes.

Molecular requirements for T cell recognition of N-myristoylated peptides derived from the simian immunodeficiency virus Nef protein

We have recently isolated a rhesus macaque cytotoxic T cell line, 2N5.1, that specifically recognizes an N-myristoylated 5-mer peptide (C(14)-Gly-Gly-Ala-Ile-Ser [C14nef5]) derived from the simian immunodeficiency virus (SIV) Nef protein. Such C14nef5-specific T cells expand in the circulation of SIV-infected monkeys, underscoring the capacity of T cells to recognize viral lipopeptides; however, the molecular basis for the lipopeptide antigen presentation remains to be elucidated. Here, functional studies indicated that the putative antigen-presenting molecule for 2N5.1 was likely to have two separate antigen-binding sites, one for interaction with a C(14)-saturated acyl chain and the other for anchorage of the C-terminal serine residue. Mutants with alanine substitutions for the second glycine residue and the fourth isoleucine residue were not recognized by 2N5.1 but interfered with the presentation of C14nef5 to 2N5.1, indicating that these structural analogues retained the ability to interact with the antigen-presenting molecules. In contrast to the highly specific recognition of C14nef5 by 2N5.1, an additional cytotoxic T cell line, SN45, established independently from a C14nef5-stimulated T cell culture, showed superb reactivity to both C14nef5 and an N-myristoylated Nef 4-mer peptide, and therefore, the C-terminal serine residue was dispensable for the recognition of lipopeptides by the SN45 T cells. Furthermore, the mutants with alanine substitutions were indeed recognized by the SN45 T cells. Given that N-myristoylation of the Nef protein occurs in the conserved motifs and is critical for viral pathogenesis, these observations predict that the lipopeptide-specific T cell response is difficult for viruses to avoid by simply introducing amino acid mutations.

Regulatory subunit myristoylation antagonizes calcineurin phosphatase activation in yeast

The Ca(2+)/calmodulin-stimulated protein phosphatase calcineurin is a critical component of Ca(2+) signaling cascades in eukaryotic cells. Myristoylation of the regulatory subunit of calcineurin (CNB) is conserved from yeast to humans. Here, we show that CNB myristoylation antagonizes phosphatase activation in yeast. Disruption of CNB myristoylation by mutation of the myristoylated glycine triggered constitutive expression of a calcineurin-dependent reporter gene and enhanced calcineurin-dependent phenotypes. Basal phosphatase activity was also increased in nmt1-181 yeast with reduced N-myristoyltransferase activity. Our findings are the first demonstration of a functional role for CNB myristoylation and reveal the importance of Nmt1 in modulating cellular calcineurin activation.

Expression and activities of N-myristoyltransferase and calcineurin in normal and inflamed lungs

The role of N-myristoyltransferase and calcineurin is well established in signaling pathways. However, there are no data on their expression and activities in normal and inflamed lungs. The mechanisms of lung inflammation induced following administration of lipopolysaccharides (LPS) or exposure to swine barn air remain unclear. Therefore, we examined expression and activities of N-myristoyltransferase and calcineurin in normal and inflamed lungs of rats. Histopathology showed acute inflammation in the lungs of rats exposed to barn air or LPS but not of control rats. There was no difference in the activities of N-myristoyltransferase and calcineurin among the control, barn-exposed, and LPS-treated rat lungs. Although N-myristoyltransferase and calcineurin were localized in airway epithelium, blood vessel walls, alveolar macrophages, and septa in the lungs of rats from all the groups, the staining intensity was increased in the lungs from rats exposed to intravenous LPS or barn air. Densitometric analyses of Western blots of 55- and 60-kDa polypeptide bands corresponding to N-myristoyltransferase and calcineurin, respectively, in the lung homogenates revealed no differences among the groups. These results show that expression of myristoyltransferase and calcineurin in lung epithelium and endothelium and a cell-specific increase in immunohistochemical expression.

Expression and activity of N-myristoyltransferase in lung inflammation of cattle and its role in neutrophil apoptosis

N-myristoyltransferase (NMT) attaches a 14 carbon fatty acid, myristic acid, to the N-terminal glycine residue of proteins. NMT exists in two isoforms NMT1 and NMT2. Myristoylated proteins play critical roles in protein-protein interactions, cell signaling and oncogenesis. Although elevated expression of NMT1 has been described in colorectal carcinoma, its expression and roles in normal and inflamed lungs of the cattle are unknown. Therefore, we investigated the expression and activity of NMT in a bovine model of lung inflammation induced with Mannheimia hemolytica and in vitro in neutrophils and macrophages. Western blots revealed increased expression of NMT1 in lungs from infected animals compared to control animals. Total NMT activity was reduced in inflamed lungs compared to control animals (p < 0.05) along with increased expression of enolase, a putative inhibitor of NMT. NMT1 staining was observed in the septum, vascular endothelium and the epithelium in the lungs from control as well as infected calves. NMT1 expression was intense in neutrophils in the necrotic areas in the inflamed lungs. Immuno-electron microscopy localized NMT1 in cytoplasm and nuclei of endothelium, pulmonary intravascular macrophages and airway epithelium. Total NMT activity and NMT1 expression were increased in neutrophils and macrophages exposed to Escherichia coli LPS in vitro. NMT knockdown increased apoptosis in activated neutrophils. This is the first report demonstrating expression of NMT in normal and inflamed lungs and a novel role for NMT in regulation of neutrophil lifespan.

Identification of differential transcript profiles between mutual crossbred embryos of zebrafish (Danio rerio) and Chinese rare minnow (Gobiocypris rarus) by cDNA-AFLP

The crosstalk between naive nucleus and maternal factors deposited in egg cytoplasm before zygotic genome activation is crucial for early development. In this study, we utilized two laboratory fishes, zebrafish (Danio rerio) and Chinese rare minnow (Gobiocypris rarus), to obtain mutual crossbred embryos and examine the interaction between nucleus and egg cytoplasm from different species. Although these two types of crossbred embryos originated from common nuclei, various developmental capacities were gained due to different origins of the egg cytoplasm. Using cDNA amplified fragment length polymorphism (cDNA-AFLP), we compared transcript profiles between the mutual crossbred embryos at two developmental stages (50%- and 90%-epiboly). Three thousand cDNA fragments were generated in four cDNA pools with 64 primer combinations. All differentially displayed transcript-derived fragments (TDFs) were screened by dot blot hybridization, and the selected sequences were further analyzed by semi-quantitative RT-PCR and quantitative real-time RT-PCR. Compared with ZR embryos, 12 genes were up-regulated and 12 were down-regulated in RZ embryos. The gene fragments were sequenced and subjected to BLASTN analysis. The sequences encoded various proteins which functioned at various levels of proliferation, growth, and development. One gene (ZR6), dramatically down-regulated in RZ embryos, was chosen for loss-of-function study; the knockdown of ZR6 gave rise to the phenotype resembling that of RZ embryos.

Biosynthesis, degradation and pharmacological importance of the fatty acid amides

The identification of two biologically active fatty acid amides, N-arachidonoylethanolamine (anandamide) and oleamide, has generated a great deal of excitement and stimulated considerable research. However, anandamide and oleamide are merely the best-known and best-understood members of a much larger family of biologically occurring fatty acid amides. In this review, we will outline which fatty acid amides have been isolated from mammalian sources, detail what is known about how these molecules are made and degraded in vivo, and highlight their potential for the development of novel therapeutics.

N-myristoyltransferase: a potential novel diagnostic marker for colon cancer

Background

Colon cancer is the second leading cause of cancer deaths in the western world. If detected early, colorectal cancer is one of the most treatable forms of cancer. Unfortunately, very few people are screened. N-myristoyltransferase (NMT) catalyzes myristoylation of various proteins including oncoproteins. We have demonstrated earlier the alteration of NMT activity during the progression of colorectal cancer and established NMT as a putative therapeutic target for cancer.

Methods

Peripheral blood samples and bone marrow were collected from the colon cancer patients and azoxymethane induced colonic tumor rats and their controls respectively. NMT activity and expression was determined as reported earlier. Immunohistochemical studies were carried out using standard procedures.

Results

In this study we demonstrate for the first time altered expression and localization of NMT in the peripheral blood and bone marrow in colon cancer patients. Immunohistochemical analysis revealed weak to negative staining for NMT in peripheral blood mononuclear cells (PBMC) of controls, whereas strong positivity was observed in PBMC colon cancer patients. In addition, we observed that NMT was localized mostly in the nuclei of the bone marrow (BM) mononuclear cells of the colon cancer patients, whereas NMT remained cytoplasmic in the control bone marrow specimens.

Conclusion

The strikingly different NMT expression offers the basis of a potential adjunct investigative tool for screening or diagnosis of patients at risk for or suspected of having colon cancer. Furthermore, altered localization of NMT in BM of tumor bearing hosts may serve as an added investigative tool for the diagnostic purpose.

Phosphorylation and dephosphorylation of human myristoyltransferase type 1

N-Myristoyltransferase (NMT) is an essential eukaryotic enzyme that catalyzes the co-translational and (or) post-translational transfer of myristate to the amino terminal glycine residue of a number of important proteins, especially the non-receptor tyrosine kinases whose activity is important for tumorigenesis. Human NMT was found to be phosphorylated by non-receptor tyrosine kinase family members of Lyn, Fyn, and Lck and dephosphorylated by the Ca2+/calmodulin-dependent protein phosphatase, calcineurin. In this review, we discuss the cross-talk that exists between NMT and their N-myristoylated protein substrates. The cross-talk among NMT, tyrosine kinases, and phosphatases may be determined by their subcellular localization and by the physiological state of the cell.

Adhesion molecules and other secreted host-interaction determinants in Apicomplexa: insights from comparative genomics

Apicomplexa have developed distinctive adaptations for invading and surviving within animal cells. Here a synthetic overview of the diversity and evolutionary history of cell membrane-associated, -secreted, and -exported proteins related to apicomplexan parasitism is presented. A notable feature in this regard was the early acquisition of adhesion protein domains and glycosylation systems through lateral transfer from animals. These were utilized in multiple contexts, including invasion of host cells and parasite-specific developmental processes. Apicomplexans possess a specialized version of the ancestral alveolate extrusion machinery, the rhoptries and micronemes, which are deployed in invasion and delivery of proteins into host cells. Each apicomplexan lineage has evolved a unique spectrum of extruded proteins that modify host molecules in diverse ways. Hematozoans, in particular, appear to have evolved novel systems for export of proteins into the host organelles and cell membrane during intracellular development. These exported proteins are an important aspect of the pathogenesis of Plasmodium and Theileria, being involved in response to fever and in leukocyte proliferation respectively. The complement of apicomplexan surface proteins has primarily diversified via massive lineage-specific expansions of certain protein families, which are often coded by subtelomeric gene arrays. Many of these families have been found to be central to immune evasion. Domain shuffling and accretion have resulted in adhesins with new domain architectures. In terms of individual genes, constant selective pressures from the host immune response has resulted in extensive protein polymorphisms and gene losses. Apicomplexans have also evolved complex regulatory mechanisms controlling expression and maturation of surface proteins at the chromatin, transcriptional, posttranscriptional, and posttranslational levels. Evolutionary reconstruction suggests that the ancestral apicomplexan had thrombospondin and EGF domain adhesins, which were linked to the parasite cytoskeleton, and played a central role in invasion through formation of the moving junction. It also suggests that the ancestral parasite had O-linked glycosylation of surface proteins which was partially or entirely lost in hematozoan lineages.

Purification and characterization of enzyme responsible for N-myristoylation of octapeptide in aqueous solution without ATP and coenzyme a from Pseudomonas aeruginosa

The enzyme that catalyzes N-acyl linkage between myristic acid and the NH(2)-terminal glycine residue of the octapeptide Gly-Asn-Ala-Ala-Ala-Ala-Arg-Arg-NH(2) in aqueous solution without ATP and coenzyme A was found in Pseudomonas aeruginosa. The enzyme was purified from cell-free crude extract using DEAE-Cellulose, Sephadex G-200, CM-Sephadex C-50, and hydroxyapatite column chromatographies, and then purified approximately 1900-fold with about 1.5% recovery of enzyme activity from the crude extract. Finally, the purified enzyme showed a main band on SDS polyacrylamide gel electrophoresis after staining with Coomassie Brilliant Blue. The band corresponded to a molecular mass of approximately 60 kDa. The K(m)s of the purified enzyme for the substrate myristic acid and the octapeptide were 0.36 and 2.6 mM, respectively. When myristoyl-CoA instead of myristic acid was used as the substrate for the enzyme reaction, myristoyl octapeptide could be synthesized as observed in the case of myristic acid. The K(m) of myristoyl-CoA was 0.17 mM.

Copper(II) and manganese(III) complexes of N'-[(2-hydroxy phenyl) carbonothioyl] pyridine-2-carbohydrazide: novel therapeutic agents for cancer

c-Src is a non-receptor tyrosine kinase which plays a significant role in the growth mediated signaling pathway impacting cellular proliferation, differentiation, mobility, survival and transformation. Myristoylation of pp60(c-src) leads to its membrane association and activation, a process catalyzed by N-myristoyltransferase (NMT). We have shown earlier increased NMT activity in the early stages of colon cancer. A novel sulfur nitrogen donor ligand and its Cu(II) and Mn(III) complexes have been prepared and characterized using various physicochemical analyses. These Cu(II) and Mn(III) complexes showed cytotoxicity against the colon cancer cell line HT29. The IC(50) for Cu(II) and Mn(III) complexes were 12.2 and 16.1 microM, respectively. HT29 cells treated with Cu(II) and Mn(III) complexes induced apoptosis and inhibited endogenous NMT activity. Furthermore, they induced higher levels of hsc70 and inhibited the expression of c-Src. Inhibition of endogenous NMT activity by metal complexes was demonstrated for the first time. This study also suggested that NMT activity is crucial for cell survival and demonstrated that cessation in activity results in apoptosis. These metal complexes may prove to be novel therapeutic agents for cancer targeting NMT.

N-myristoyltransferase 2 expression in human colon cancer: cross-talk between the calpain and caspase system

A number of viral and eukaryotic proteins which undergo a lipophilic modification by the enzyme N-myristoyltransferase (NMT: NMT1 and NMT2) are required for signal transduction and regulatory functions. To investigate whether NMT2 contributes to the pathogenesis of colorectal carcinoma, we observed a higher expression of NMT2 in most of the cases of cancerous tissues compared to normal tissues (84.6% of cases; P < 0.05) by Western blot analysis. Furthermore, protein-protein interaction of NMTs revealed that m-calpain interacts with NMT1 while caspase-3 interacts with NMT2. Our findings provide the first evidence of higher expression of NMT2 in human colorectal adenocarcinomas and the interaction of both forms of NMT with various signaling molecules.

Effects of lactate dehydrogenase suppression and glycerol-3-phosphate dehydrogenase overexpression on cellular metabolism

In order to conduct a physiological functional study of lactate dehydrogenase (LDH) and glycerol-3-phosphate dehydrogenase (GPDH), we engineered a CHO dhfr(-) cell, by overexpressing either the anti-sense LDH-A RNA (anti-LDH cells) or GPDH (GP3 cells), or both (GP3/anti-LDH cells). LDH activity in the cell cytosol, and lactate content and pHe change in the growth media were found to decrease according to the order: cell lines GP3/anti-LDH > anti-LDH > GP3 > CHO. Intracellular ATP contents, representing the extent of respiration rate, also decreased, according to a rank order as follows: GP3 > CHO > GP3/anti-LDH > anti-LDH. We also attempted to identify and characterize any physiological changes occurring in the cells which harbored diverse metabolic pathways. First, anti-LDH cells with heightened respiration rates were found to display a higher degree of sensitivity to the prooxidant tert-butyl hydroperoxide (tBOOH), and the mitochondrial complex III inhibitor, antimycin A, than the GPDH-expressing cells (GP3 and GP3/anti-LDH), which have a lower respiration rate. Second, the anti-sense LDH-A RNA-expressing cells (anti-LDH and GP3/anti-LDH) evidenced a higher degree of resistance to apoptosis by cell-cell contact inhibition, and a faster doubling time ( approximately 19 h compared with approximately 26 h) than the CHO and GP3 cells. Additionally, cell growth in an extended culture under HCO(3) (-)-free conditions to induce a steep acidification could be maintained with the anti-sense LDH-A RNA-expressing cells, but could not be maintained with the CHO and GP3 cells. Third, we observed that the most appropriate cell line for the optical production of a certain therapeutic protein (Tissue-Plasminogen Activator) was the GP3/anti-LDH cells. Collectively, our data indicate a variety of physiological roles for LDH and GPDH, including cellular acidosis, oxidoresistance, apoptosis by both acidosis and cell-cell contact inhibition, cell growth, and the generation of recombinant proteins.

A live cell, image-based approach to understanding the enzymology and pharmacology of 2-bromopalmitate and palmitoylation

The addition of a lipid moiety to a protein increases its hydrophobicity and subsequently its attraction to lipophilic environments like membranes. Indeed most lipid-modified proteins are localized to membranes where they associate with multiprotein signaling complexes. Acylation and prenylation are the two common categories of lipidation. The enzymology and pharmacology of prenylation are well understood but relatively very little is known about palmitoylation, the most common form of acylation. One distinguishing characteristic of palmitoylation is that it is a dynamic modification. To understand more about how palmitoylation is regulated, we fused palmitoylation substrates to fluorescent proteins and reported their subcellular distribution and trafficking. We used automated high-throughput fluorescence microscopy and a specialized computer algorithm to image and measure the fraction of palmitoylation reporter on the plasma membrane versus the cytoplasm. Using this system we determined the residence half-life of palmitate on the dipalmitoyl substrate peptide from GAP43 as well as the EC(50) for 2-bromopalmitate, a common inhibitor of palmitoylation.

Expression of myristoyltransferase and its interacting proteins in epilepsy

N-Myristoylation is a co-translational, irreversible addition of a fatty acyl moiety to the amino terminus of many eukaryotic cellular proteins. This modification is catalyzed by N-myristoyltransferase (NMT) and is recognized to be a widespread and functionally important modification of proteins. The myristoylated Src family kinases are involved in various signaling cascades, including the N-methyl-d-aspartate receptor functions. We examined the expression of NMT and its interacting proteins to gain further insight into the mechanisms in epileptic fowl. Higher expression of NMT1 and NMT2 was observed in carrier and epileptic fowl whereas expression of heat shock cognate protein 70, an inhibitor of NMT, was lower. Furthermore, protein-protein interaction of NMT with m-calpain, caspase-3, and p53 was established. The interaction of NMT2 with caspase-3 and p53 was weak in epileptic fowl compared with normal chicks while the interaction of NMT1 with m-calpain was weak in epileptics. Understanding the regulation of NMT by specific inhibitors may help us to control the action of this enzyme on its specific substrates and may lead to improvements in the management of various neurological disorders like Alzheimer's disease, ischemia, and epilepsy.

Potential role of N-myristoyltransferase in pathogenic conditions

N-Myristoyltransferase (NMT) is the enzyme that catalyzes the covalent transfer of myristic acid to the N-terminal glycine residue of a protein substrate. In this review article, I summarize that NMT may have a potential role in cardiac muscle in the experimentally induced ischemia-reperfusion rat model and also in the streptozotoein-induced diabetic rat. Both the expression and activity of NMT were increased by ischemia-reperfusion. Immunohistochemical studies showed cytosolic localization of NMT in normal rat heart and predominant nuclear localization after ischemia followed by reperfusion. However, the localization of NMT is reversed by treatment with a calpain inhibitor (ALLM N-Ac-Leu-Leu-methioninal). During ischemia-reperfusion, the degradation of c-Src, which is a substrate of NMT, was observed. These findings suggested that the Src signaling may be impaired in ischemia-reperfusion owing to the altered localization of NMT from cytoplasm to nucleus. Streptozotocin-induced diabetes (an animal model for insulin-dependent diabetes mellitus) resulted in a 2.0-fold increase in rat liver NMT activity as compared with control animals. In obese (fa/fa) Zucker rats (an animal model for non-insulin-dependent diabetes mellitus), there was an approximately 4.7-fold lower liver particulate NMT activity as compared with control lean rat livers. Administration of sodium orthovanadate to the diabetic rats normalized liver NMT activity. These results would indicate that rat liver particulate NMT activity appears to be inversely proportional to the level of plasma insulin, implicating insulin in the control of N-myristoylation. These are the first studies demonstrating the role of NMT in the pathogenesis of ischemia-reperfusion and diabetes mellitus. These conditions remain an important area of investigation.

High expression of methionine aminopeptidase 2 in human colorectal adenocarcinomas

PURPOSE

Several viral and eukaryotic proteins required for signal transduction and regulatory functions undergo lipophilic modification by the enzyme N-myristoyltransferase. Previously we reported that N-myristoyltransferase activity is higher in colon and gallbladder carcinoma than in the corresponding normal tissues. Methionine aminopeptidase 2 (MetAP2) is a bifunctional protein that plays a critical role in the regulation of post-translational processing and protein synthesis. To investigate whether MetAP2 contributes to the pathogenesis of colon carcinoma, we investigated the expression of MetAP2 in both normal and invasive tumor components of human samples.

EXPERIMENTAL DESIGN

We evaluated 50 cases of colon carcinoma for this study. In this report we analyzed 15 cases for MetAP2 activity and 13 cases for the expression of MetAP2 by Western blot in both the normal and in invasive tumor components of human samples. In addition, immunohistochemistry analysis was also carried out on samples from all patients.

RESULTS

MetAP activity was elevated in all cancerous tissues compared with normal tissues. Western blot analysis also showed the higher expression of MetAP2 in all cases of cancerous tissues. In addition, immunohistochemistry analysis revealed that all cases of colorectal adenocarcinoma showed moderate to strong cytoplasmic positivity for MetAP2 with increased intensity in the invasive component.

CONCLUSIONS

Elevated MetAP protein expression is associated with metastatic tumor progression and appears to be a strong molecular marker for clinical prognosis. MetAP2 inhibition may represent a potential target for therapeutic intervention in colorectal carcinoma.

Myristoylation of the RING finger Z protein is essential for arenavirus budding

The arenavirus small RING finger Z protein is the main driving force of arenavirus budding. The primary structure of Z is devoid of hydrophobic transmembrane domains, but both lymphocytic choriomeningitis virus (LCMV) and Lassa fever virus Z proteins accumulate near the inner surface of the plasma membrane and are strongly membrane associated. All known arenavirus Z proteins contain a glycine (G) at position 2, which is a potential acceptor site for a myristoyl moiety. Metabolic labeling showed incorporation of [(3)H]myristic acid by wild-type Z protein but not by the G2A mutant. The mutation G2A eliminated Z-mediated budding. Likewise, treatment with the myristoylation inhibitor 2-hydroxymyristic acid inhibited Z-mediated budding, eliminated formation of virus-like particles, and caused a dramatic reduction in virus production in LCMV-infected cells. Budding activity was restored in G2A mutant Z proteins by the addition of the myristoylation domain of the tyrosine protein kinase Src to their N termini. These findings indicate N-terminal myristoylation of Z plays a key role in arenavirus budding.

Expression of methionine aminopeptidase 2, N-myristoyltransferase, and N-myristoyltransferase inhibitor protein 71 in HT29

Protein myristoylation is a co-translational process, catalyzed by N-myristoyltransferase (NMT) that occurs after the initiating methionine is removed by methionine aminopeptidase (MetAP). The enzymes NMT and MetAP play a major role in the process of myristoylation of oncoproteins including the c-src family. In this study, we examined the levels of expression of MetAP2, NMT, and NMT inhibitor protein 71 (NIP71) in human colon cancer cell lines (HCCLs). We examined the influence of cell density on the expression of the above proteins in HT29 cells. Western blot analysis of MetAP2 and NMT demonstrated higher levels of protein expression in low density of HT29 while low expression in high density was observed. In addition, we observed that NIP71 and pp60(c-src) expressions were dependent on the cell density of HT29. This is the first study demonstrating the expression of MetAP2, NMT, pp60(c-src), and NIP71 in HCCLs.

MYRbase: analysis of genome-wide glycine myristoylation enlarges the functional spectrum of eukaryotic myristoylated proteins

We evaluated the evolutionary conservation of glycine myristoylation within eukaryotic sequences. Our large-scale cross-genome analyses, available as MYRbase, show that the functional spectrum of myristoylated proteins is currently largely underestimated. We give experimental evidence for in vitro myristoylation of selected predictions. Furthermore, we classify five membrane-attachment factors that occur most frequently in combination with, or even replacing, myristoyl anchors, as some protein family examples show.

A novel inhibitor protein of N-myristoyltransferase from Escherichia coli

Myristoyl-CoA:protein N-myristoyltransferase (NMT) catalyzes the covalent attachment of myristate to the N-terminal of the glycine residue of various eukaryotic and viral proteins of diverse functions. Earlier, we have demonstrated that NMT activity is elevated in colon and gall bladder cancer. Attenuation of NMT activity may prove a novel therapeutic protocol for cancer. We report here a novel inhibitor protein of NMT being expressed in Escherichia coli cells containing the human NMT gene on increasing the incubation period from 5 to 24h. The inhibitor protein was purified by SP-Sepharose column chromatography, heat treatment, ammonium sulfate precipitation, and Superose 12 HR/30 FPLC column chromatography. The inhibitor protein had an apparent molecular mass of 10kDa by gel filtration. It inhibited human NMT in a concentration-dependent manner with 50% inhibition at 640+/-4.68nM. The inhibitor protein showed no direct interaction with myristoyl-CoA and demonstrated no demyristoylase or protease activity. Therefore, we conclude that the inhibitor protein acts directly on NMT.

Expression of the genes (, , , , and ) in

The luxA, B, C, D, and E genes from Photorhabdus luminescens were cloned and functionally expressed in Saccharomyces cerevisiae to construct a bacterial lux-based yeast bioreporter capable of autonomous bioluminescence emission. The bioreporter was engineered using a series of pBEVY yeast expression vectors that allowed for bi-directional constitutive or inducible expression of the individual luxA, B, C, and E genes. The luxD gene, encoding the acyl-ACP transferase that ultimately supplies the requisite aldehyde substrate for the bioluminescent reaction, was fused to a yeast internal ribosomal entry site (IRES) sequence to ensure high bi-cistronic expression. Although self-generation of bioluminescence was achieved by the bioreporter, the signal was relatively weak and decayed rapidly. To overcome this instability, a flavin oxidoreductase gene (frp) from Vibrio harveyi was co-expressed to provide sufficient concentrations of the FMNH(2) co-factor required for the bioluminescent reaction. Expression of frp with the lux genes not only stabilized but also enhanced bioluminescence to levels approaching 9.0x10(5) times above background.

Characterization of human palmitoyl-acyl transferase activity using peptides that mimic distinct palmitoylation motifs

The covalent attachment of palmitate to proteins commonly occurs on cysteine residues near either N-myristoylated glycine residues or C-terminal farnesylated cysteine residues. It therefore seems likely that multiple palmitoyl-acyl transferase (PAT) activities exist to recognize and modify these distinct palmitoylation motifs. To evaluate this possibility, two synthetic peptides representing these palmitoylation motifs, termed MyrGCK(NBD) and FarnCNRas(NBD), were used to characterize PAT activity under a variety of conditions. The human tumour cell lines MCF-7 and Hep-G2 each demonstrated high levels of PAT activity towards both peptides. In contrast, normal mouse fibroblasts (NIH/3T3 cells) demonstrated PAT activity towards the myristoylated substrate peptide but not the farnesylated peptide, while ras -transformed NIH/3T3 cells were able to palmitoylate the FarnCNRas(NBD) peptide. The kinetic parameters for PAT activity were determined using membranes from MCF-7 cells, and indicated that the K (m) values for palmitoyl-CoA were identical for PAT activity towards the two substrate peptides; however, the K (m) for MyrGCK(NBD) was 5-fold lower than the K (m) for FarnCNRas(NBD). PAT activity towards the two substrate peptides was dose-dependently inhibited by 2-bromopalmitate and 3-(1-oxo-hexadecyl)oxiranecarboxamide (16C; IC(50) values of approx. 4 and 1.3 microM, respectively); however, 2-bromopalmitate was found to be uncompetitive with respect to palmitoyl-CoA, whereas 16C was competitive. To seek additional evidence for multiple PATs, the effects of altering the assay conditions on the palmitoylation of MyrGCK(NBD) and FarnCNRas(NBD) were compared. PAT activity towards the two peptide substrates was modulated similarly by changing the ionic strength or incubation temperature, or by the addition of dithiothreitol. In contrast, the enzymic palmitoylation of the two peptides was differentially affected by N -ethylmaleimide and thermal denaturation. Overall, these data demonstrate that the enzymic palmitoylation of farnesyl- and myristoyl-containing peptide substrates can be differentiated, suggesting that multiple motif-specific PATs exist.

Altered expression and localization of N-myristoyltransferase in experimentally induced rat model of ischemia-reperfusion

N-myristoyltransferase (NMT) catalyzes the attachment of myristate onto the amino-terminal glycine residue of select polypeptides. In the present study, we investigated the expression and activity of NMT in rat heart after ischemia and reperfusion. Western blot analysis of rat heart samples indicated a prominent immunoreactive band of 66 kDa probed with human NMT antibody. Both the expression and activity of NMT were increased by ischemia-reperfusion. Immunohistochemical studies showed cytosolic localization of NMT in normal rat heart and predominant nuclear localization after ischemia followed by reperfusion. The pre-ischemic perfusion and post-ischemic reperfusion of hearts with a cell-permeable calpain inhibitor (N-Ac-Leu-Leu-methioninal) suppressed the increase in calpain expression and reversed the localization of NMT from nucleus to cytoplasm. This is the first study demonstrating the expression and alteration of NMT localization in cardiac ischemia and pertaining to a possible role of co-translational modification of proteins in cardiac functions and injury.

Role of palmitoylation/depalmitoylation reactions in G-protein-coupled receptor function

G-protein-coupled receptors (GPCRs) constitute one of the largest protein families in the human genome. They are subject to numerous post-translational modifications, including palmitoylation. This review highlights the dynamic nature of palmitoylation and its role in GPCR expression and function. The palmitoylation of other proteins involved in GPCR signaling, such as G-proteins, regulators of G-protein signaling, and G-protein-coupled receptor kinases, is also discussed.

Enhanced activity of human N-myristoyltransferase by dimethyl sulfoxide and related solvents in the presence of serine/threonine-containing peptide substrates

Human N-myristoyltransferase (hNMT) activity was found to be stimulated several-fold by DMSO and its analogues in the presence of serine-containing peptide substrates. DMSO caused a concentration-dependent 10-fold stimulation of hNMT activity in the presence of a pp60(src)-derived peptide substrate (Gly-Ser-Ser-Lys-Ser-Lys-Pro-Lys-Arg). However, the stimulation of hNMT activity was not observed by DMSO when a cyclic AMP (cAMP)-dependent protein kinase-derived Ser-free peptide substrate (Gly-Asn-Ala-Ala-Ala-Ala-Lys-Lys-Arg-Arg) was used. These findings suggested that the effect of DMSO is on the substrate rather than on the enzyme. When a MARCKS (myristoylated alanine-rich C-kinase substrate)-derived peptide substrate (Gly-Ala-Gln-Phe-Ser-Lys-Thr-Ala-Arg-Arg) and the M2 gene segment of the reovirus type 3 peptide substrate (Gly-Asn-Ala-Ser-Ser-Ile-Lys-Lys-Lys) were used, hNMT activity was increased by approximately 8.5- and 7-fold, respectively. Dimethyl sulfone (20%) increased hNMT activity between 2.5- and 3.5-fold in the presence of pp60(src), MARCKS, and M2 gene segment peptides. Dimethyl formamide (20%) increased the hNMT activity by 8.5-, 8.5-, 5.5- and 3.5-fold when pp60(src), MARCKS, M2, and cAMP-dependent protein kinase-derived peptide substrates were used, respectively. Acetone (20%) also increased the hNMT activity by 20-fold in the presence of the pp60(src) peptide substrate. Dimethyl ammonium chloride (20%) caused about 6.5- and 2.5-fold increases in the hNMT activity in the presence of the pp60(src) and cAMP-dependent protein kinase-derived peptide substrates, respectively. Infrared spectroscopy showed a decreased intensity in the band at 3500-3600cm(-1) when the infrared spectrum of the pp60(src)-derived peptide was determined in the presence of DMSO. These results suggest the involvement of hydrogen bonding between the heteroatoms of the organic molecules and the hydrogen atoms of the free hydroxyl groups of the serine/threonine-containing peptide substrates. Such interactions appear to enhance the activity of hNMT towards its serine-containing substrates.

A fluorescence-based high performance liquid chromatographic method for the characterization of palmitoyl acyl transferase activity

Although protein palmitoylation is essential for targeting many important signaling proteins to the plasma membrane, the mechanism by which palmitoylation occurs is uncharacterized, since the enzyme(s) responsible for this modification remain unidentified. To study palmitoyl acyl transferase (PAT) activity, we developed an in vitro palmitoylation (IVP) assay using a fluorescently labeled substrate peptide, mimicking the N-terminal palmitoylation motif of proteins such as non-receptor Src-related tyrosine kinases. The palmitoylated and non-palmitoylated forms of the peptide were resolved by reverse-phase HPLC and detected by fluorescence. The method was optimized for PAT activity using lysates from the MCF-7 and Hep-G2 human tumor cell lines. The PAT activity was inhibited by boiling, reducing the incubation temperature, or adding 10 microM 2-bromopalmitate, a known palmitoylation inhibitor. This IVP assay provides the first method that is suitable to study all facets of the palmitoylation reaction, including peptide palmitoylation by PAT(s), depalmitoylation by thioesterases, and evaluation of potential palmitoylation inhibitors.

Antifungals targeted to protein modification: focus on protein N-myristoyltransferase

Invasive fungal infections have increased dramatically in recent years to become important causes of morbidity and mortality in hospitalised patients. Currently available antifungal drugs for such infections essentially have three molecular targets: 14 alpha demethylase (azoles), ergosterol (polyenes) and beta-1,3-glucan synthase (echinocandins). The first is a fungistatic target vulnerable to resistance development; the second, while a fungicidal target, is not sufficiently different from the host to ensure high selectivity; the third, a fungistatic (Aspergillus) or fungicidal (Candida) target, has limited activity spectrum (gaps: Cryptococcus, emerging fungi) and potential host toxicity that might preclude dose escalation. Drugs aimed at totally new targets are thus needed to increase our chemotherapeutic options and to forestall, alone or in combination chemotherapy, the emergence of drug resistance. Protein N-myristoylation, the cotranslational transfer of the 14-carbon saturated fatty acid myristate from CoA to the amino-terminal glycine of several fungal proteins such as the ADP-ribosylation factor (ARF), presents such an attractive new target. The reaction, catalysed by myristoyl-CoA:protein N-myristoyltransferase (NMT), is essential for viability, is biochemically tractable and has proven potential for selectivity. In the past five years, a number of selective inhibitors of the fungal enzyme, some with potent, broad spectrum antifungal activity, have been reported: myristate analogues, myristoylpeptide derivatives, histidine analogues (peptidomimetics), aminobenzothiazoles, quinolines and benzofurans. A major development has been the publication of the crystal structure of Candida albicans and Saccharomyces cerevisiae NMTs, which has allowed virtual docking of inhibitors on the enzyme and refinement of structure-activity relationships of lead compounds.

N-terminal N-myristoylation of proteins: refinement of the sequence motif and its taxon-specific differences

N-terminal N-myristoylation is a lipid anchor modification of eukaryotic and viral proteins targeting them to membrane locations, thus changing the cellular function of modified proteins. Protein myristoylation is critical in many pathways; e.g. in signal transduction, apoptosis, or alternative extracellular protein export. The myristoyl-CoA:protein N-myristoyltransferase (NMT) recognizes the sequence motif of appropriate substrate proteins at the N terminus and attaches the lipid moiety to the absolutely required N-terminal glycine residue. Reliable recognition of capacity for N-terminal myristoylation from the substrate protein sequence alone is desirable for proteome-wide function annotation projects but the existing PROSITE motif is not practical, since it produces huge numbers of false positive and even some false negative predictions. As a first step towards a new prediction method, it is necessary to refine the sequence motif coding for N-terminal N-myristoylation. Relying on the in-depth study of the amino acid sequence variability of substrate proteins, on binding site analyses in X-ray structures or 3D homology models for NMTs from various taxa, and on consideration of biochemical data extracted from the scientific literature, we found indications that, at least within a complete substrate protein, the N-terminal 17 protein residues experience different types of variability restrictions. We identified three motif regions: region 1 (positions 1-6) fitting the binding pocket; region 2 (positions 7-10) interacting with the NMT's surface at the mouth of the catalytic cavity; and region 3 (positions 11-17) comprising a hydrophilic linker. Each region was characterized by physical requirements to single sequence positions or groups of positions regarding volume, polarity, backbone flexibility and other typical properties of amino acids (http://mendel.imp.univie.ac.at/myristate/). These specificity differences are confined partly to taxonomic ranges and are proposed for the design of NMT inhibitors in pathogenic fungal and protozoan systems including Aspergillus fumigatus, Leishmania major, Trypanosoma cruzi, Trypanosoma brucei, Giardia intestinalis, Entamoeba histolytica, Pneumocystis carinii, Strongyloides stercoralis and Schistosoma mansoni. An exhaustive search for NMT-homologues led to the discovery of two putative entomopoxviral NMTs.

Cytotoxic 1,4-bis(2-oxo-1-cycloalkylmethylene)benzenes and related compounds

A series of 1,4-bis(2-oxo-1-cycloalkylmethylene)benzenes 2a-c and 4 and a related acyclic analogue 6a were synthesised and converted to the corresponding Mannich bases 3a-c, 5 and 6b. Evaluation of these compounds against murine P388 and L1210 cells as well as human Molt 4/C8 and CEM T-lymphocytes revealed that the Mannich bases were more cytotoxic than the corresponding unsaturated ketones. 1,4-bis(3-Dimethylaminomethyl-2-oxo-1-cyclohexylmethylene)benzene dihydrochloride (3a) had lower IC(50) values than melphalan against the four cell lines and was 15 times more potent than this drug when examined against a panel of human tumours.

Phosphorylation of human N-myristoyltransferase by N-myristoylated SRC family tyrosine kinase members

N-Myristoyltransferase (NMT) is an essential eukaryotic enzyme that catalyzes the cotranslational and/or posttranslational transfer of myristate to the amino terminal glycine residue of a number of important proteins especially the non-receptor tyrosine kinases whose activity is important for tumorigenesis. Human NMT was found to be phosphorylated by non-receptor tyrosine kinase family members of Lyn, Fyn and Lck and dephosphorylated by the Ca(2+)/calmodulin-dependent protein phosphatase, calcineurin. Deletion of 149 amino acids from the N-terminal end resulted in the absence of phosphorylation suggesting that the phosphorylation sites are located in the N-terminal end of NMT. Furthermore, a site-directed mutagenesis study indicated that substitution of tyrosine 100 with phenylalanine served NMT as a poor substrate for the Lyn kinase. A synthetic peptide corresponding to the amino-terminal region encompassing tyrosine 100 of NMT served as a good substrate for the Lyn and Fyn kinases. Our studies also indicated that NMT was found to interact with Lyn through its N-terminal end in a phosphorylation-dependent manner. This is the first study demonstrating the cross-talk between NMT and their myristoylated protein substrates in signaling pathways.