Protein tyrosine phosphorylation in Mycobacterium tuberculosis

Mycobacterium tuberculosis and its secreted tyrosine phosphatases

Tuberculosis is one of the most common infectious diseases and has been a major burden for a long time now. Increasing drug resistance in TB is slowing down the process of disease treatment. Mycobacterium tuberculosis, the causative agent of TB is known to have a cascade of virulence factors to fight with host's immune system. The phosphatases (PTPs) of Mtb plays a critical role as these are secretory in nature and help the survival of bacteria in host. Researchers have been trying to synthesize inhibitors against a lot of virulence factors of Mtb but recently the phosphatases have gained a lot of interest due to their secretory nature. This review gives a concise overview of virulence factors of Mtb with emphasis on mPTPs. Here we discuss the current scenario of drug development against mPTPs.

Identification of Arginine Phosphorylation in Mycolicibacterium smegmatis

Tuberculosis is a leading cause of worldwide infectious mortality. The prevalence of multidrug-resistant Mycobacterium tuberculosis infections drives an urgent need to exploit new drug targets. One such target is the ATP-dependent protease ClpC1P1P2, which is strictly essential for viability. However, few proteolytic substrates of mycobacterial ClpC1P1P2 have been identified to date. Recent studies in Bacillus subtilis have shown that the orthologous ClpCP protease recognizes proteolytic substrates bearing posttranslational arginine phosphorylation. While several lines of evidence suggest that ClpC1P1P2 is similarly capable of recognizing phosphoarginine-bearing proteins, the existence of phosphoarginine modifications in mycobacteria has remained in question. Here, we confirm the presence of posttranslational phosphoarginine modifications in Mycolicibacterium smegmatis, a nonpathogenic surrogate of M. tuberculosis. Using a phosphopeptide enrichment workflow coupled with shotgun phosphoproteomics, we identified arginine phosphosites on several functionally diverse targets within the M. smegmatis proteome. Interestingly, phosphoarginine modifications are not upregulated by heat stress, suggesting divergent roles in mycobacteria and Bacillus. Our findings provide new evidence supporting the existence of phosphoarginine-mediated proteolysis by ClpC1P1P2 in mycobacteria and other actinobacterial species. IMPORTANCE Mycobacteria that cause tuberculosis infections employ proteolytic pathways that modulate cellular behavior by destroying specific proteins in a highly regulated manner. Some proteolytic enzymes have emerged as novel antibacterial targets against drug-resistant tuberculosis infections. However, we have only a limited understanding of how these enzymes function in the cell and how they select proteins for destruction. Some proteolytic enzymes are capable of recognizing proteins that carry an unusual chemical modification, arginine phosphorylation. Here, we confirm the existence of arginine phosphorylation in mycobacterial proteins. Our work expands our understanding of a promising drug target in an important global pathogen.

Hydrolyzable tannins (ellagitannins), flavonoids, pentacyclic triterpenes and their glycosides in antimycobacterial extracts of the ethnopharmacologically selected Sudanese medicinal plant Combretum hartmannianum Schweinf

In Sudanese traditional medicine, decoctions, macerations, and tonics of the stem and root of Combretum hartmannianum are used for the treatment of persistent cough, a symptom that could be related to tuberculosis (TB). To verify these traditional uses, extracts from the stem wood, stem bark, and roots of C. hartmannianum were screened for their growth inhibitory effects against Mycobacterium smegmatis ATCC 14468. Methanol Soxhlet and ethyl acetate extracts of the root gave the strongest effects (MIC 312.5 and 625 µg/ml, respectively). HPLC-UV/DAD and UHPLC/QTOF-MS analysis of the ethyl acetate extract of the root led to the detection of 54 compounds, of which most were polyphenols and many characterized for the first time in C. hartmannianum. Among the major compounds were terflavin B and its two isomers, castalagin, corilagin, tellimagrandin I and its derivative, (S)-flavogallonic acid dilactone, punicalagin, and methyl-ellagic acid xylopyranoside. In addition, di-, tri- and tetra-galloyl glucose, combregenin, terminolic acid, cordifoliside D, luteolin, and quercetin-3-O-galactoside-7-O-rhamnoside-(2→1)-O-β-D-arabinopyranoside were characterized. Luteolin gave better growth inhibition against M. smegmatis (MIC 250 µg/ml) than corilagin, ellagic acid, and gallic acid (MIC 500-1000 µg/ml). Our study justifies the use of C. hartmannianum in Sudanese folk medicine against prolonged cough that could be related to TB infection. This study demonstrates that C. hartmannianum should be explored further for new anti-TB drug scaffolds and antibiotic adjuvants.

Distinct epigenetic regulation in patients with multidrug-resistant TB-HIV co-infection and uninfected individuals

BACKGROUND

Mycobacterium tuberculosis (Mtb) is an airborne pathogenic microorganism that causes tuberculosis (TB). This pathogen invades lung tissues causing pulmonary infections and disseminates into other host organs. The Bacillus Calmette-Guérin (BCG) vaccine is employed to provide immune protection against TB; however, its efficacy is dependent on the age, immune status and geographic location of vaccinated individuals. Advanced diagnostic approaches such as GeneXpert MTB/RIF® and line probe assays (LPAs) have allowed rapid detection of drug-resistant, multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mtb strains. However, in sub-Saharan Africa, public and private health institutions are further burdened by the high prevalence of Human Immunodeficiency Virus (HIV), the causative agent of acquired immunodeficiency syndrome (AIDS) and TB co-infections across different age groups. Epigenetic mechanisms have been widely exploited by Mtb and HIV to bypass the host's innate and adaptive immune responses, leading to microbial proliferation and disease manifestation. In the current study, we investigated the impact of epigenetic mechanisms in regulating target gene expression in healthy and patients co-infected with MDR TB-HIV.

Examining the levels of acetylation, DNA methylation and phosphorylation in HIV-1 positive and multidrug-resistant TB-HIV patients

OBJECTIVES

In this study, we examined the impact of epigenetic modifications on host gene functioning by assessing the expression of seven candidate genes in three separate groups including healthy, multidrug-resistant (MDR) TB-HIV co-infected and HIV-1 positive individuals.

METHODS

Ten patients with MDR TB and HIV-1 co-infection on TB and HIV therapy and a cohort comprised of 10 newly diagnosed individuals with HIV-1 infection were recruited from the TB and HIV clinics at the Charlotte Maxeke Johannesburg Academic Hospital. Notably, the HIV-1 positive individuals were not placed on antiretroviral therapy (ART) at the time of recruitment and blood collection. A third group consisting of 10 healthy participants without MDR TB or HIV infection was recruited from the University of the Witwatersrand. Blood samples collected from all three cohorts were employed for extraction of plasma, total RNA and genomic DNA.

RESULTS

Our data indicated that the expression of DNA methyltransferase 1 (DNMT1) and Ten-eleven translocation methylcytosine dioxygenase 1 (TET1) genes was significantly increased in HIV-1 positive patients and was lowest in MDR TB-HIV co-infected patients. By contrast, histone acetyltransferase (HAT), histone deacetylase (HDAC), protein tyrosine kinase (PtkA) and protein tyrosine phosphatase (PtpA) mRNA expression levels were substantially enhanced in HIV-1 infected and were lowest in healthy individuals. Conversely, Dicer expression levels were comparable among all three study groups.

CONCLUSION

Promising preliminary data emanating from this investigation may potentially be used for generation of novel vaccines and therapeutic compounds capable of neutralising MDR TB-HIV and HIV-1 infection.

Identification of differential protein recognition pattern between Naegleria fowleri and Naegleria lovaniensis

Many pathogenicity factors are involved in the development of primary amoebic meningoencephalitis (PAM) caused by N fowleri. However, most of them are not exclusive for N fowleri and they have not even been described in other nonpathogenic Naegleria species. Therefore, the objective of this work was to identify differential proteins and protein pattern recognition between Naegleria fowleri and Naegleria lovaniensis using antibodies anti-N fowleri as strategy to find vaccine candidates against meningoencephalitis. Electrophoresis and Western blots conventional and 2-DE were performed for the identification of antigenic proteins, and these were analysed by the mass spectrometry technique. The results obtained in 2-DE gels and Western blot showed very notable differences in spot intensity between these two species, specifically those with relative molecular weight of 100, 75, 50 and 19 kDa. Some spots corresponding to these molecular weights were identified as actin fragment, myosin II, heat shock protein, membrane protein Mp2CL5 among others, with differences in theoretical post-translational modifications. In this work, we found differences in antigenic proteins between both species, proteins that could be used for a further development of vaccines against N fowleri infection.

Long-range replica exchange molecular dynamics guided drug repurposing against tyrosine kinase PtkA of Mycobacterium tuberculosis

Tuberculosis (TB) is a leading cause of death worldwide and its impact has intensified due to the emergence of multi drug-resistant (MDR) and extensively drug-resistant (XDR) TB strains. Protein phosphorylation plays a vital role in the virulence of Mycobacterium tuberculosis (M.tb) mediated by protein kinases. Protein tyrosine phosphatase A (MptpA) undergoes phosphorylation by a unique tyrosine-specific kinase, protein tyrosine kinase A (PtkA), identified in the M.tb genome. PtkA phosphorylates PtpA on the tyrosine residues at positions 128 and 129, thereby increasing PtpA activity and promoting pathogenicity of MptpA. In the present study, we performed an extensive investigation of the conformational behavior of the intrinsically disordered domain (IDD) of PtkA using replica exchange molecular dynamics simulations. Long-term molecular dynamics (MD) simulations were performed to elucidate the role of IDD on the catalytic activity of kinase core domain (KCD) of PtkA. This was followed by identification of the probable inhibitors of PtkA using drug repurposing to block the PtpA-PtkA interaction. The inhibitory role of IDD on KCD has already been established; however, various analyses conducted in the present study showed that IDD_PtkA had a greater inhibitory effect on the catalytic activity of KCD_PtkA in the presence of the drugs esculin and inosine pranobex. The binding of drugs to PtkA resulted in formation of stable complexes, indicating that these two drugs are potentially useful as inhibitors of M.tb.

Mycobacterium tuberculosis serine/threonine protein kinases: structural information for the design of their specific ATP-competitive inhibitors

In the last decades, human protein kinases (PKs) have been relevant as targets in the development of novel therapies against many diseases, but the study of Mycobacterium tuberculosis PKs (MTPKs) involved in tuberculosis pathogenesis began much later and has not yet reached an advanced stage of development. To increase knowledge of these enzymes, in this work we studied the structural features of MTPKs, with focus on their ATP-binding sites and their interactions with inhibitors. PknA, PknB, and PknG are the most studied MTPKs, which were previously crystallized; ATP-competitive inhibitors have been designed against them in the last decade. In the current work, reported PknA, PknB, and PknG inhibitors were extracted from literature and their orientations inside the ATP-binding site were proposed by using docking method. With this information, interaction fingerprints were elaborated, which reveal the more relevant residues for establishing chemical interactions with inhibitors. The non-crystallized MTPKs PknD, PknF, PknH, PknJ, PknK, and PknL were also studied; their three-dimensional structural models were developed by using homology modeling. The main characteristics of MTPK ATP-binding sites (the non-crystallized and crystallized MTPKs, including PknE and PknI) were accounted; schemes of the main polar and nonpolar groups inside their ATP-binding sites were constructed, which are suitable for a major understanding of these proteins as antituberculotic targets. These schemes could be used for establishing comparisons between MTPKs and human PKs in order to increase selectivity of MTPK inhibitors. As a key tool for guiding medicinal chemists interested in the design of novel MTPK inhibitors, our work provides a map of the structural elements relevant for the design of more selective ATP-competitive MTPK inhibitors.

The domain architecture of PtkA, the first tyrosine kinase from Mycobacterium tuberculosis, differs from the conventional kinase architecture

The discovery that MptpA (low-molecular-weight protein tyrosine phosphatase A) from Mycobacterium tuberculosis (Mtb) has an essential role for Mtb virulence has motivated research of tyrosine-specific phosphorylation in Mtb and other pathogenic bacteria. The phosphatase activity of MptpA is regulated via phosphorylation on Tyr128 and Tyr129 Thus far, only a single tyrosine-specific kinase, protein-tyrosine kinase A (PtkA), encoded by the Rv2232 gene has been identified within the Mtb genome. MptpA undergoes phosphorylation by PtkA. PtkA is an atypical bacterial tyrosine kinase, as its sequence differs from the sequence consensus within this family. The lack of structural information on PtkA hampers the detailed characterization of the MptpA-PtkA interaction. Here, using NMR spectroscopy, we provide a detailed structural characterization of the PtkA architecture and describe its intra- and intermolecular interactions with MptpA. We found that PtkA's domain architecture differs from the conventional kinase architecture and is composed of two domains, the N-terminal highly flexible intrinsically disordered domain (IDDPtkA) and the C-terminal rigid kinase core domain (KCDPtkA). The interaction between the two domains, together with the structural model of the complex proposed in this study, reveal that the IDDPtkA is unstructured and highly dynamic, allowing for a "fly-casting-like" mechanism of transient interactions with the rigid KCDPtkA This interaction modulates the accessibility of the KCDPtkA active site. In general, the structural and functional knowledge of PtkA gained in this study is crucial for understanding the MptpA-PtkA interactions, the catalytic mechanism, and the role of the kinase-phosphatase regulatory system in Mtb virulence.

Structural characterization of the intrinsically disordered domain of Mycobacterium tuberculosis protein tyrosine kinase A

Although intrinsically disordered proteins or protein domains (IDPs or IDD) are less abundant in bacteria than in eukaryotes, their presence in pathogenic bacterial proteins is important for protein-protein interactions. The protein tyrosine kinase A (PtkA) from Mycobacterium tuberculosis possesses an 80-residue disordered region (IDD_PtkA ) of unknown function, located N-terminally to the well-folded kinase core domain. Here, we characterize the conformation of IDD_PtkA under varying biophysical conditions and phosphorylation using NMR-spectroscopy. Our results confirm that the N-terminal domain of PtkA exists as an IDD at physiological pH. Furthermore, phosphorylation of IDD_PtkA increases the activity of PtkA. Our findings will complement future approaches in understanding molecular mechanisms of key proteins in pathogenic virulence.

Protein tyrosine kinase, PtkA, is required for Mycobacterium tuberculosis growth in macrophages

Protein phosphorylation plays a key role in Mycobacterium tuberculosis (Mtb) physiology and pathogenesis. We have previously shown that a secreted protein tyrosine phosphatase, PtpA, is essential for Mtb inhibition of host macrophage acidification and maturation, and is a substrate of the protein tyrosine kinase, PtkA, encoded in the same operon. In this study, we constructed a ∆ptkA deletion mutant in Mtb and found that the mutant exhibited impaired intracellular survival in the THP-1 macrophage infection model, correlated with the strain's inability to inhibit macrophage phagosome acidification. By contrast, the mutant displayed increased resistance to oxidative stress in vitro. Proteomic and transcriptional analyses revealed upregulation of ptpA, and increased secretion of TrxB2, in the ΔptkA mutant. Kinase and protein-protein interaction studies demonstrated that TrxB2 is a substrate of PtkA phosphorylation. Taken together these studies establish a central role for the ptkA-ptpA operon in Mtb pathogenesis.

Epigenetic Phosphorylation Control of Mycobacterium tuberculosis Infection and Persistence

Reversible protein phosphorylation is the most common type of epigenetic posttranslational modification in living cells used as a major regulation mechanism of biological processes. The Mycobacterium tuberculosis genome encodes for 11 serine/threonine protein kinases that are responsible for sensing environmental signals to coordinate a cellular response to ensure the pathogen's infectivity, survival, and growth. To overcome killing mechanisms generated within the host during infection, M. tuberculosis enters a state of nonreplicating persistence that is characterized by arrested growth, limited metabolic activity, and phenotypic resistance to antimycobacterial drugs. In this article we focus our attention on the role of M. tuberculosis serine/threonine protein kinases in sensing the host environment to coordinate the bacilli's physiology, including growth, cell wall components, and central metabolism, to establish a persistent infection.

Phosphorylation of Mycobacterium tuberculosis protein tyrosine kinase A PtkA by Ser/Thr protein kinases

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), has inflicted about one third of mankind and claims millions of deaths worldwide annually. Signalling plays an important role in Mtb pathogenesis and persistence, and thus represents attractive resource for drug target candidates. Here, we show that protein tyrosine kinase A (PtkA) can be phosphorylated by Mtb endogenous eukaryotic-like Ser/Thr protein kinases (eSTPKs). Kinase assays showed that PknA, PknD, PknF, and PknK can phosphorylate PtkA in dose- and time-dependent manner. Enzyme kinetics suggests that PknA has the highest affinity and enzymatic efficiency towards PtkA. Furthermore, protein-protein interaction assay in surrogate host showed that PtkA interacts with multi-eSTPKs in vivo, including PknA. Lastly, we show that PtkA phosphorylation by eSTPKs occurs on threonine residues and may effect tyrosine phosphorylation levels and thus PtkA activity in vitro. These results demonstrate that PtkA can serve as a substrate to many eSTPKs and suggests that's its activity can be regulated.

Screening of Microbial Extracts for Anticancer Compounds Using Streptomyces Kinase Inhibitor Assay

Eukaryotic kinases are known to play an important role in signal transduction pathways by phosphorylating their respective substrates. Abnormal phosphorylations by these kinases have resulted in diseases. Hence inhibitors of kinases are of considerable pharmaceutical interest for a wide variety of disease targets, especially cancers. A number of reports have been published which indicate that eukaryotic-like kinases may complement two-component kinase systems in several bacteria. In Streptomyces sp. such kinases have been found to have a role in formation of aerial hyphae, spores, pigmentation & even in antibiotic production in some strains. Eukaryotic kinase inhibitors are seen to inhibit formation of aerial mycelia in Streptomyces without inhibiting vegetative mycelia. This property has been used to design an assay to screen for eukaryotic kinase inhibitors. The assay involves testing of compounds against Streptomyces 85E ATCC 55824 using agar well diffusion method. Inhibitors of kinases give rise to “bald” colonies where aerial mycelia and sporulation inhibition is seen. The assay has been standardized using known eukaryotic protein kinase inhibiting anticancer agents like AG-490, AG-1295, AG-1478, Flavopiridol and Imatinib as positive controls, at a concentration ranging from 10 μg/well to 100 μg/well. Anti-infective compounds which are not reported to inhibit eukaryotic protein kinases were used as negative controls. A number of microbial cultures have been screened for novel eukaryotic protein kinase inhibitors. Further these microbial extracts were tested in various cancer cell lines like Panc1, HCT116, Calu1, ACHN and H460 at a concentration of 10 μg/mL/ well. The anticancer data was seen correlating well with the Streptomyces kinase assay thus validating the assay.

Mycobacterium tuberculosis supports protein tyrosine phosphorylation

Reversible protein phosphorylation determines growth and adaptive decisions in Mycobacterium tuberculosis (Mtb). At least 11 two-component systems and 11 Ser/Thr protein kinases (STPKs) mediate phosphorylation on Asp, His, Ser, and Thr. In contrast, protein phosphorylation on Tyr has not been described previously in Mtb. Here, using a combination of phospho-enrichment and highly sensitive mass spectrometry, we show extensive protein Tyr phosphorylation of diverse Mtb proteins, including STPKs. Several STPKs function as dual-specificity kinases that phosphorylate Tyr in cis and in trans, suggesting that dual-specificity kinases have a major role in bacterial phospho-signaling. Mutation of a phosphotyrosine site of the essential STPK PknB reduces its activity in vitro and in live Mtb, indicating that Tyr phosphorylation has a functional role in bacterial growth. These data identify a previously unrecognized phosphorylation system in a human pathogen that claims ∼ 1.4 million lives every year.

Bacterial tyrosine kinases: evolution, biological function and structural insights

Reversible protein phosphorylation is a major mechanism in the regulation of fundamental signalling events in all living organisms. Bacteria have been shown to possess a versatile repertoire of protein kinases, including histidine and aspartic acid kinases, serine/threonine kinases, and more recently tyrosine and arginine kinases. Tyrosine phosphorylation is today recognized as a key regulatory device of bacterial physiology, linked to exopolysaccharide production, virulence, stress response and DNA metabolism. However, bacteria have evolved tyrosine kinases that share no resemblance with their eukaryotic counterparts and are unique in exploiting the ATP/GTP-binding Walker motif to catalyse autophosphorylation and substrate phosphorylation on tyrosine. These enzymes, named BY-kinases (for Bacterial tYrosine kinases), have been identified in a majority of sequenced bacterial genomes, and to date no orthologues have been found in Eukarya. The aim of this review was to present the most recent knowledge about BY-kinases by focusing primarily on their evolutionary origin, structural and functional aspects, and emerging regulatory potential based on recent bacterial phosphoproteomic studies.

Protein kinase and phosphatase signaling in Mycobacterium tuberculosis physiology and pathogenesis

Mycobacterium tuberculosis (Mtb), the etiological agent of tuberculosis (TB), evades the antimicrobial defenses of the host and survives within the infected individual through a complex set of strategies. These include active prevention of host cellular killing processes as well as overwhelming adaptive gene expression. In the past decade, we have gained an increased understanding of how mycobacteria not only have the ability to adapt to a changing host environment but also actively interfere with the signaling machinery within the host cell to counteract or inhibit parts of the killing apparatus employed by the macrophage. Mtb is able to sense its environment via a set of phospho-signaling proteins which mediate its response and interaction with the host in a coordinated manner. In this review, we summarize the current knowledge about selected Mtb serine, threonine, and tyrosine kinase and phosphatase signaling proteins, focusing on the protein kinases, PknG and PtkA, and the protein phosphatase, PtpA.

Mycobacterium tuberculosis PtkA is a novel protein tyrosine kinase whose substrate is PtpA

In Mycobacterium tuberculosis, signal transduction is mediated by 11 serine/threonine kinases, but no tyrosine kinases have been identified thus far. The protein encoded by the ORF (open reading frame) Rv2232 has been annotated as a member of the HAD (haloacid dehydrogenase-like hydrolase) superfamily, which includes phosphatases, phosphomanno- and phosphogluco-mutases, and haloacid dehydrogenases. In the present paper, we report, on the basis of biochemical and mutational analyses, that the Rv2232-encoded protein, named protein tyrosine kinase A (PtkA) is a bona fide protein tyrosine kinase. The cognate substrate of PtkA is the secreted protein tyrosine phosphatase A (PtpA).

Tyrosine-kinases in bacteria: from a matter of controversy to the status of key regulatory enzymes

When considering protein phosphorylation in bacteria, phosphorylation of aspartic acid and histidine residues mediated by the two-component systems is the first to spring to mind. And yet other phosphorylation systems have been described in bacteria in the past 20 years including eukaryotic-like serine/threonine kinases and more recently tyrosine-kinases. Among the latter, a peculiar type is widespread among bacteria, but not in higher organisms. These enzymes possess unique structural features defining thus a new family of enzymes termed Bacterial tyrosine kinases (BY-kinases). BY-kinases have been shown to be mainly involved in polysaccharide production, but their ability to phosphorylate endogenous substrates indicates that they participate in the regulation of other functions of the bacterial cell. Recent advances in mass spectrometry based phosphoproteomics provided lists of many new phosphotyrosine-proteins, indicating that BY-kinases may be involved in regulating a large array of other cellular functions. One may expect that in a near future, tyrosine phosphorylation will turn out to be one of the key regulatory processes in the bacterial cell and will yield new insights into the understanding of its physiology.

Targeting the PTPome in human disease

Protein tyrosine phosphatases (PTPs) play vital roles in numerous cellular processes and are implicated in a growing number of human diseases, ranging from cancer to cardiovascular, immunological, infectious, neurological and metabolic diseases. There are at least 107 genes in the human genome, collectively referred to as the human 'PTPome'. Here the authors review the involvement of PTPs in human disease, discuss their potential as drug targets, and current efforts to develop PTP inhibitors for the treatment of human disease. Finally, the authors present their view of the future for PTPs as drug targets.

Mycobacterial manipulation of the host cell

Phagosome biogenesis, the process by which macrophages neutralize ingested pathogens and initiate antigen presentation, has entered the field of cellular mycobacteriology research largely owing to the discovery 30 years ago that phagosomes harboring mycobacteria are refractory to fusion with lysosomes. In the past decade, the use of molecular genetics and biology in different model systems to study phagosome biogenesis have made significant advances in understanding subtle mechanisms by which mycobacteria inhibit the maturation of its phagosome. Thus, we are beginning to appreciate the extent to which these pathogens are able to interfere with innate immune responses and manipulate defense mechanisms to enhance their survival within the human host cell. Here, we summarize current knowledge about phagosome maturation arrest in infected macrophages and the subsequent attenuation of the macrophage-initiated adaptive anti-mycobacterial immune defenses.

Low-molecular-weight protein tyrosine phosphatases of Bacillus subtilis

In gram-negative organisms, enzymes belonging to the low-molecular-weight protein tyrosine phosphatase (LMPTP) family are involved in the regulation of important physiological functions, including stress resistance and synthesis of the polysaccharide capsule. LMPTPs have been identified also in gram-positive bacteria, but their functions in these organisms are presently unknown. We cloned two putative LMPTPs from Bacillus subtilis, YfkJ and YwlE, which are highly similar to each other in primary structure as well as to LMPTPs from gram-negative bacteria. When purified from overexpressing Escherichia coli strains, both enzymes were able to dephosphorylate p-nitrophenyl-phosphate and phosphotyrosine-containing substrates in vitro but showed significant differences in kinetic parameters and sensitivity to inhibitors. Transcriptional analyses showed that yfkJ was transcribed at a low level throughout the growth cycle and underwent a sigma(B)-dependent transcriptional upregulation in response to ethanol stress. The transcription of ywlE was growth dependent but stress insensitive. Genomic deletion of each phosphatase-encoding gene led to a phenotype of reduced bacterial resistance to ethanol stress, which was more marked in the ywlE deletion strain. Our study suggests that YfkJ and YwlE play roles in B. subtilis stress resistance.

Autophosphorylation of the 16 kDa and 70 kDa antigens (Hsp 16.3 and Hsp 70) of Mycobacterium tuberculosis

Several antigens of Mycobacterium tuberculosis, identified by monoclonal antibodies, have been previously cloned and are being exploited in the development of improved vaccines and diagnostic reagents. In this study, the molecular characteristics of two of these antigens, the immunodominant proteins Hsp 16.3 and Hsp 70, were analysed in further detail by assessing their capacity to undergo protein phosphorylation, a chemical modification frequently used by organisms to adjust to environmental variations. Hsp 16.3 was overproduced in an Escherichia coli expression system and purified to homogeneity. Upon incubation in the presence of radioactive ATP, it was shown to possess autophosphorylation activity. Two-dimensional analysis of its phosphoamino acid content revealed that it was modified exclusively at serine residues. In addition, cross-linking experiments demonstrated that it could tightly bind to ATP. Purified Hsp 70 was also shown to autophosphorylate but phosphorylation occurred exclusively at threonine residues. This reaction was found to be strongly stimulated by calcium ions. These data indicate that both structural and functional similarities exist between Hsp 16.3 (Acr) and alpha-crystallin, a eukaryotic protein which plays an important role in maintaining the transparency of the vertebrate eye, and that the functional properties of Hsp 70 from M. tuberculosis are similar to those of other bacterial members of the Hsp 70 family, particularly the E. coli homologue DnaK.

PknH, a transmembrane Hank's type serine/threonine kinase from Mycobacterium tuberculosis is differentially expressed under stress conditions

Serine/threonine protein kinases (STPKs) represent a burgeoning concept in prokaryotic signaling and have been implicated in a range of control mechanisms. This paper describes the enzymatic and molecular characterization of PknH, a mycobacterial STPK. After cloning and expression as a Glutathione-S-transferase fusion protein in E. coli, PknH was found to phosphorylate itself and exogenous substrates like myelin basic protein and histone. The kinase activity of PknH was inhibited by the kinase inhibitors staurosporine and H-7. The results confirmed that PknH is a transmembrane protein and is restricted to members of the Mycobacterium tuberculosis complex. In addition, transcriptional analysis of pknH in M. tuberculosis under various stress conditions revealed that exposure to low pH and heat shock decreased the level of pknH transcription significantly. This is the first report describing differential expression of a mycobacterial kinase in response to stress conditions which can indicate its ability to regulate cellular events promoting bacterial adaptation to environmental change.

Apparent growth phase-dependent phosphorylation of malonyl coenzyme A:acyl carrier protein transacylase (MCAT), a major fatty acid synthase II component inMycobacterium bovisBCG

Probing protein extracts from exponentially growing and stationary phase cultures of Mycobacterium bovis BCG with anti-phospho amino acid antibodies revealed a 31-kDa anti-phospho threonine antibody-reactive protein specific to growing culture. The corresponding protein was purified via two-dimensional gel electrophoresis and identified via mass spectrometry to be malonyl coenzyme A:acyl carrier protein transacylase (MCAT), a component of the fatty acid biosynthetic pathway. MCAT tagged with histidine reacted with anti-phospho threonine antibody and was positive in an in-gel chemical assay for phospho proteins. Analysis of the growth phase dependence of MCAT-His phosphorylation and protein levels showed that phosphorylated MCAT-His can be detected only in growing culture. In contrast, MCAT-His protein level was growth phase-independent. These results suggest that MCAT may be a substrate of a protein kinase and phosphatase, and that aspects of fatty acid synthesis in tubercle bacilli are regulated by protein phosphorylation.

Expression and localization of the Mycobacterium tuberculosis protein tyrosine phosphatase PtpA

The Mycobacterium tuberculosis open reading frame Rv2234 encodes a low molecular weight tyrosine phosphatase named PtpA. Kinetic analyses of PtpA activity reveal that it is capable of dephosphorylation of p-nitrophenyl phosphate, as well as a variety of phosphotyrosine-containing substrates. In contrast, PtpA showed no detectable activity towards substrates containing phosphoserine or -threonine residues. Transcriptional analysis reveals that the M. tuberculosis ptpA promoter is expressed in the slow-growing Mycobacterium species M. bovis BCG, but not in the fast-growing species M. smegmatis. Furthermore, ptpA expression is upregulated upon entry of BCG cultures into stationary phase and increases upon infection of human monocytes. We also show that, despite the lack of a general export pathway signal sequence, the M. tuberculosis PtpA protein can be released from both M. tuberculosis and M. smegmatis during growth.

Serine/threonine protein kinases PknF and PknG of Mycobacterium tuberculosis: characterization and localization

Pathogenesis of Mycobacterium tuberculosis is closely connected to its survival and replication within the host. Some pathogenic bacteria employ protein kinases that interfere with the cellular signalling network of host cells and promote bacterial survival. In this study, the pknF and pknG genes, which encode two putative protein kinases of M. tuberculosis H(37)Rv, protein kinase F (PknF) and protein kinase G (PknG), respectively, were cloned and expressed in Escherichia coli. Purified PknF phosphorylated the peptide substrate myelin basic protein (MBP) at serine and threonine residues, while purified PknG phosphorylated only at serine residues. The activity of the two kinases was abrogated by mutation of the codon for the predicted ATP-binding-site lysine residue. Southern blot analysis revealed that homologues of the genes encoding the two kinases are present in M. tuberculosis H(37)Ra and Mycobacterium bovis BCG, but not in Mycobacterium smegmatis. Immunoblot analysis of various cellular fractions of M. tuberculosis H(37)Rv revealed that PknF is a transmembrane protein and that PknG is predominantly a cytosolic enzyme. The present study should aid in elucidating the role of these protein kinases in the pathogenesis of mycobacteria.

The eukaryotic-like Ser/Thr protein kinases of Mycobacterium tuberculosis

In bacteria, extracellular signals are generally transduced into cellular responses via a two-component system. However, genome sequence data have now revealed the presence of 'eukaryotic-like' protein kinases and phosphatases. Mycobacterium tuberculosis appears to be unique among bacteria in that its genome contains 11 members of a newly identified protein kinase family. These M. tuberculosis eukaryotic-like protein kinases could be key regulators of metabolic processes, including transcription, cell development and interactions with host cells.