Molecular and functional characterization of adenylate kinase 2 gene from Leishmania donovani

Deficiency in AK9 causes asthenozoospermia and male infertility by destabilising sperm nucleotide homeostasis

BACKGROUND

Asthenozoospermia is the primary cause of male infertility; however, its genetic aetiology remains poorly understood. Adenylate kinase 9 (AK9) is highly expressed in the testes of humans and mice and encodes a type of adenosine kinase that is functionally involved in cellular nucleotide homeostasis and energy metabolism. We aimed to assess whether AK9 is involved in asthenozoospermia.

METHODS

One-hundred-and-sixty-five Chinese men with idiopathic asthenozoospermia were recruited. Whole-exome sequencing (WES) and Sanger sequencing were performed for genetic analyses. Papanicolaou staining, Haematoxylin and eosin staining, scanning electron microscopy, and transmission electron microscopy were used to observe the sperm morphology and structure. Ak9-knockout mice were generated using CRISPR-Cas9. Sperm adenosine was detected by liquid chromatography-mass spectrometry. Targeted sperm metabolomics was performed. Intracytoplasmic sperm injection (ICSI) was used to treat patients.

FINDINGS

We identified five patients harbouring bi-allelic AK9 mutations. Spermatozoa from men harbouring bi-allelic AK9 mutations have a decreased ability to sustain nucleotide homeostasis. Moreover, bi-allelic AK9 mutations inhibit glycolysis in sperm. Ak9-knockout male mice also presented similar phenotypes of asthenozoospermia. Interestingly, ICSI was effective in bi-allelic AK9 mutant patients in achieving good pregnancy outcomes.

INTERPRETATION

Defects in AK9 induce asthenozoospermia with defects in nucleotide homeostasis and energy metabolism. This sterile phenotype could be rescued by ICSI.

FUNDING

The National Natural Science Foundation of China (82071697), Medical Innovation Project of Fujian Province (2020-CXB-051), open project of the NHC Key Laboratory of Male Reproduction and Genetics in Guangzhou (KF202004), Medical Research Foundation of Guangdong Province (A2021269), Guangdong Provincial Reproductive Science Institute Innovation Team grants (C-03), and Outstanding Young Talents Program of Capital Medical University (B2205).

Molecular characterization and immunological properties of Echinococcus granulosus sensu stricto (G1) ADK1 and ADK8

Adenylate kinases (ADKs) are one of the important enzymes regulating adenosine triphosphate (ATP) metabolism in Echinococcus granulosus sensu lato. The objective of the present study was to explore the molecular characteristics and immunological properties of E. granulosus sensu stricto (G1) adenylate kinase 1 (EgADK1) and adenylate kinase 8 (EgADK8). EgADK1 and EgADK8 were cloned and expressed, and the molecular characteristics of EgADK1 and EgADK8 were analyzed through different bioinformatics tools. Western blotting was used to examine the reactogenicity of recombinant adenylate kinase 1 (rEgADK1) and recombinant adenylate kinase 8 (rEgADK8) and to evaluate their diagnostic value. The expression profiles of EgADK1 and EgADK8 in 18-day-old strobilated worms and protoscoleces were analyzed by quantitative real-time PCR, and their distribution in 18-day-old strobilated worms, the germinal layer, and protoscoleces was determined by immunofluorescence localization. EgADK1 and EgADK8 were successfully cloned and expressed. Bioinformatics analysis predicted that EgADK1 and EgADK8 have multiple phosphorylation sites and B-cell epitopes. Compared with EgADK8, EgADK1 and other parasite ADKs have higher sequence similarity. In addition, both cystic echinococcosis (CE)-positive sheep sera and Cysticercus tenuicollis-infected goat sera could recognize rEgADK1 and rEgADK8. EgADK1 and EgADK8 were localized in protoscoleces, the germinal layer, and 18-day-old strobilated worms. EgADK1 and EgADK8 showed no significant difference in their transcription level in 18-day-old strobilated worms and protoscoleces, suggesting that EgADK1 and EgADK8 may play an important role in the growth and development of E. granulosus sensu lato. Since EgADK1 and EgADK8 can be recognized by other parasite-positive sera, they are not suitable as candidate antigens for the diagnosis of CE.

Comparative phosphoproteomic analysis unravels MAPK1 regulated phosphoproteins in Leishmania donovani

Mitogen Activated Protein Kinase1 (MAPK1) of Leishmania donovani functions as key regulators of various cellular activities, which seem to be imperative for parasite survival, infectivity, drug resistance and post-translational modification of chaperones/co-chaperones. However, very less is known about LdMAPK1 target proteins. With recent advancements in proteomics, we aimed to identify phosphoproteins which were differentially expressed in LdMAPK1 overexpressing (Dd8++/++) and single replacement mutants (Dd8+/) as compared to wild type (Dd8+/+) parasites, utilizing LC-MS/MS approach. An in-depth label-free phospoproteomic analysis revealed that modulation of LdMAPK1 expression significantly modulates expression levels of miscellaneous phosphoproteins which may act as its targets/substrates. Out of 1974 quantified phosphoproteins in parasite, 140 were significantly differentially expressed in MAPK1 overexpressing and single replacement mutants. These differentially expressed phosphoproteins are majorly associated with metabolism, signal transduction, replication, transcription, translation, transporters and cytoskeleton/motor proteins, hence suggested that MAPK1 may act in concert to modulate global biological processes. The study further implicated possible role of LdMAPK1 in regulation and management of stress machinery in parasite through post translational modifications. Precisely, comparative phosphoproteomics study has elucidated significant role of LdMAPK1 in regulating various pathways contributing in parasite biology with relevance to future drug development. SIGNIFICANCE: MAPKinase1, the downstream kinase of MAPK signal transduction pathway, has drawn much attention as potential therapeutic drug target due to their indispensable role in survival and infectivity of Leishmania donovani. However, limited information is available about its downstream effector proteins/signaling networks. Utilizing label free LC-MS/MS analysis, phosphoproteome of LdMAPK1 over-expressing (Dd8++/++) and LdMAPK1 single replacement mutants (Dd8+/-) with wild type (Dd8+/+) parasites was compared and identified 140 LdMAPK1 modulated phosphoproteins, mainly involved in pathways like signal transduction, metabolism, transcriptional, translational, post-translational modification and regulation of heat shock proteins. Interestingly, LdMAPK1 interacts directly with only six phosphoproteins i.e. casein kinase, casein kinase II, HSP83/HSP90, LACK, protein kinase and serine/threonine protein kinase. Thus, the study elucidates significant role of LdMAPK1 in Leishmania biology which may drive drug-discovery efforts against visceral leishmaniasis.

Kinetic and oligomeric study of Leishmania braziliensis nicotinate/nicotinamide mononucleotide adenylyltransferase

Nicotinamide adenine dinucleotide (NAD) is an essential coenzyme involved in REDOX reactions and oxidative stress defense systems. Furthermore, NAD is used as substrate by proteins that regulate essential cellular functions as DNA repair, genetic, and signal transduction, among many others. NAD biosynthesis can be completed through the de novo and salvage pathways, which converge at the common step catalyzed by the nicotinate/nicotinamide mononucleotide adenylyltransferase (NMNAT EC: 2.7.7.1/18). Here, we report the kinetic characterization of the NMNAT of Leishmania braziliensis (LbNMNAT), one of the etiological agents of leishmaniasis, a relevant parasitic disease. The expression and homogeneous purification of the recombinant 6xHis-LbNMNAT protein was carried out and its kinetic study, which included analysis of K m , V max , K cat and the equilibrium constant (K D ) for both the forward and reverse reactions, was completed. The oligomeric state of the recombinant 6xHis-LbNMNAT protein was studied through size exclusion chromatography. Our results indicated the highest and lowest K m values for ATP and NAD, respectively. According to the calculated K D , the pyrophosphorolytic cleavage of NAD is favored in vitro. Moreover, the recombinant 6xHis-LbNMNAT protein showed a monomeric state, although it exhibits a structural element involved in potential subunits interaction. Altogether, our results denote notable differences of the LbNMNAT protein in relation to the human orthologs HsNMNAT1-3. These differences constitute initial findings that have to be continued to finally propose the NMNAT as a promissory pharmacological target in L. braziliensis.

Leishmania donovani adenylate kinase 2a prevents ATP-mediated cell cytolysis in macrophages

In Leishmania spp. ATP utilizing enzymes serves as a key role in preserving integrity of host cells for survival of parasite. Earlier reports suggested that Adenylate kinase (AK) a phosphotransferase enzyme released by Leishmania donovani secretome, involved in modulating levels of NTPs. In the present study, we cloned, expressed and characterized recombinant putative AK. Based on a sequence and phylogeny analysis, we identified the prominent features of the seven AK isoforms of Leishmania donovani and assigned our putative AK as LdAK2a. The K_m value of LdAK2a for ATP and AMP substrate were 204 μM and 184 μM, respectively and V_max was calculated as 1.6 μmol min^-1 mg^-1 protein. Ap5A, a known inhibitor of AK inhibited LdAK2a with estimated K_i values of 280 nM and 230 nM for ATP and AMP respectively. CD spectral studies were carried out to estimate its structural stability. Recombinant LdAK2a was found to prevent ATP mediated cell cytolysis of Raw 264.7 macrophages in vitro, which was determined by LDH assay and MMP assay. This is the first report which validates that Leishmanial AK2a can prevent ATP mediated cytolysis of macrophage cells and thereby probably play a role in preserving integrity of host cells for survival of parasite.

In Search of Biomarkers for Pathogenesis and Control of Leishmaniasis by Global Analyses of Leishmania-Infected Macrophages

Leishmaniasis is a vector-borne, neglected tropical disease with a worldwide distribution that can present in a variety of clinical forms, depending on the parasite species and host genetic background. The pathogenesis of this disease remains far from being elucidated because the involvement of a complex immune response orchestrated by host cells significantly affects the clinical outcome. Among these cells, macrophages are the main host cells, produce cytokines and chemokines, thereby triggering events that contribute to the mediation of the host immune response and, subsequently, to the establishment of infection or, alternatively, disease control. There has been relatively limited commercial interest in developing new pharmaceutical compounds to treat leishmaniasis. Moreover, advances in the understanding of the underlying biology of Leishmania spp. have not translated into the development of effective new chemotherapeutic compounds. As a result, biomarkers as surrogate disease endpoints present several potential advantages to be used in the identification of targets capable of facilitating therapeutic interventions considered to ameliorate disease outcome. More recently, large-scale genomic and proteomic analyses have allowed the identification and characterization of the pathways involved in the infection process in both parasites and the host, and these analyses have been shown to be more effective than studying individual molecules to elucidate disease pathogenesis. RNA-seq and proteomics are large-scale approaches that characterize genes or proteins in a given cell line, tissue, or organism to provide a global and more integrated view of the myriad biological processes that occur within a cell than focusing on an individual gene or protein. Bioinformatics provides us with the means to computationally analyze and integrate the large volumes of data generated by high-throughput sequencing approaches. The integration of genomic expression and proteomic data offers a rich multi-dimensional analysis, despite the inherent technical and statistical challenges. We propose that these types of global analyses facilitate the identification, among a large number of genes and proteins, those that hold potential as biomarkers. The present review focuses on large-scale studies that have identified and evaluated relevant biomarkers in macrophages in response to Leishmania infection.

Using Proteomics to Understand How Leishmania Parasites Survive inside the Host and Establish Infection

Leishmania is a protozoan parasite that causes a wide range of different clinical manifestations in mammalian hosts. It is a major public health risk on different continents and represents one of the most important neglected diseases. Due to the high toxicity of the drugs currently used, and in the light of increasing drug resistance, there is a critical need to develop new drugs and vaccines to control Leishmania infection. Over the past few years, proteomics has become an important tool to understand the underlying biology of Leishmania parasites and host interaction. The large-scale study of proteins, both in parasites and within the host in response to infection, can accelerate the discovery of new therapeutic targets. By studying the proteomes of host cells and tissues infected with Leishmania, as well as changes in protein profiles among promastigotes and amastigotes, scientists hope to better understand the biology involved in the parasite survival and the host-parasite interaction. This review demonstrates the feasibility of proteomics as an approach to identify new proteins involved in Leishmania differentiation and intracellular survival.

AMP promotes oxygen consumption and ATP synthesis in heart mitochondria through the adenylate kinase reaction: an NMR spectroscopy and polarography study

Adenylate kinase plays an important role in cellular energy homeostasis by catalysing the interconversion of adenine nucleotides. The goal of present study was to evaluate the contribution of the adenylate kinase reaction to oxidative ATP synthesis by direct measurements of ATP using (31) P NMR spectroscopy. Results show that AMP can stimulate ATP synthesis in the presence or absence of ADP. In particular, addition of 1 mM AMP to the 0.6 mM ADP superfusion system of isolated superfused mitochondria (contained and maintained in agarose beads) led to a 25% increase in ATP synthesis as measured by the increase in βATP signal. More importantly, we show that AMP can support ATP synthesis in the absence of ADP, demonstrated as follows. Superfusion of mitochondria without ADP led to the disappearance of ATP γ, α and β signals and the increase of Pi . Addition of AMP to the medium restored the production of ATP, as demonstrated by the reappearance of γ, α and β ATP signals, in conjunction with a decrease in Pi , which is being used for ATP synthesis. Polarographic studies showed Mg(2+) dependence of this process, confirming the specificity of the adenylate kinase reaction. Furthermore, data obtained from this study demonstrate, for the first time, that different aspects of the adenylate kinase reaction can be evaluated with (31) P NMR spectroscopy. SIGNIFICANCE OF RESEARCH PARAGRAPH: The data generated in the present study indicate that (31) P NMR spectroscopy can effectively be used to study the adenylate kinase reaction under a variety of conditions. This is important because understanding of adenylate kinase function and/or malfunction is essential to understanding its role in health and disease. The data obtained with (31) P NMR were confirmed by polarographic studies, which further strengthens the robustness of the NMR findings. In summary, (31) P NMR spectroscopy provides a sensitive tool to study adenylate kinase activity in different physiological and pathophysiological conditions, including but not exclusive of, cancer, ischemic injury, hemolytic anemia and neurological problems such as sensorineural deafness.

A quantitative proteomic screen to identify potential drug resistance mechanism in α-difluoromethylornithine (DFMO) resistant Leishmania donovani

Visceral leishmaniasis (VL) caused by Leishmania donovani is a systemic protozoan disease that is fatal if left untreated. The promastigote form of L. donovani is sensitive to growth inhibition by dl-α-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (ODC), the first enzyme of the polyamine biosynthetic pathway. Exposure of a wild type (DI700) cell population to gradually increasing concentrations of DFMO resulted in the selection of a strain of Leishmania (DFMO-16), which was capable of proliferating in 16mM DFMO. To elucidate the molecular basis for this resistance, we undertook a comparative proteomic analysis of DFMO-resistant/sensitive parasites using isobaric tagging for relative and absolute quantification (iTRAQ/LC-MS/MS). Out of the 101 proteins identified in at least 2 of the 3 independent experiments, 82 proteins are 1.5- to 44.0-fold more abundant in DFMO-resistant strain (DFMO-16) while 19 are 2- to 5.0-fold less abundant as compared to the wild-type (DI700) parasites. Proteins with 2-fold or greater abundance in the DFMO-resistant strain include free radical detoxification, polyamine and trypanothione metabolic proteins, proteins involved in metabolism, intracellular survival and proteolysis, elongation factors, signaling molecules and mitochondrial transporters, and many with no annotated function. Differentially modulated proteins contribute to our understanding of molecular mechanism of DFMO-resistance and have the potential to act as biomarkers.

BIOLOGICAL SIGNIFICANCE

This study will facilitate a deeper understanding of the phenomenon of acquired drug resistance and possible biomarkers in Leishmania against antiparasitic drug DFMO. Also it will provide information about the metabolic pathways modulated in resistant parasites as an adaptation mechanism to counter drugs. Studies like this are important to safeguard the efficacy of a limited repertoire of anti-parasitic drugs, and to lead the development of new drugs and drug combinations.

The DUSP26 phosphatase activator adenylate kinase 2 regulates FADD phosphorylation and cell growth

Adenylate kinase 2 (AK2), which balances adenine nucleotide pool, is a multi-functional protein. Here we show that AK2 negatively regulates tumour cell growth. AK2 forms a complex with dual-specificity phosphatase 26 (DUSP26) phosphatase and stimulates DUSP26 activity independently of its AK activity. AK2/DUSP26 phosphatase protein complex dephosphorylates fas-associated protein with death domain (FADD) and regulates cell growth. AK2 deficiency enhances cell proliferation and induces tumour formation in a xenograft assay. This anti-growth function of AK2 is associated with its DUSP26-stimulating activity. Downregulation of AK2 is frequently found in tumour cells and human cancer tissues showing high levels of phospho-FADD(Ser194). Moreover, reconstitution of AK2 in AK2-deficient tumour cells retards both cell proliferation and tumourigenesis. Consistent with this, AK2(+/-) mouse embryo fibroblasts exhibit enhanced cell proliferation with a significant alteration in phospho-FADD(Ser191). These results suggest that AK2 is an associated activator of DUSP26 and suppresses cell proliferation by FADD dephosphorylation, postulating AK2 as a negative regulator of tumour growth.

Molecular and functional characterization of a Trypanosoma cruzi nuclear adenylate kinase isoform

Trypanosoma cruzi, the etiological agent of Chagas' disease, is an early divergent eukaryote in which control of gene expression relies mainly in post-transcriptional mechanisms. Transcription levels are globally up and down regulated during the transition between proliferating and non-proliferating life-cycle stages. In this work we characterized a nuclear adenylate kinase isoform (TcADKn) that is involved in ribosome biogenesis. Nuclear adenylate kinases have been recently described in a few organisms, being all related to RNA metabolism. Depending on active transcription and translation, TcADKn localizes in the nucleolus or the cytoplasm. A non-canonical nuclear localization signal was mapped towards the N-terminal of the protein, being the phosphate-binding loop essential for its localization. In addition, TcADKn nuclear exportation depends on the nuclear exportation adapter CRM1. TcADKn nuclear shuttling is governed by nutrient availability, oxidative stress and by the equivalent in T. cruzi of the mammalian TOR (Target of Rapamycin) pathway. One of the biological functions of TcADKn is ribosomal 18S RNA processing by direct interaction with ribosomal protein TcRps14. Finally, TcADKn expression is regulated by its 3′ UTR mRNA. Depending on extracellular conditions, cells modulate protein translation rates regulating ribosome biogenesis and nuclear adenylate kinases are probably key components in these processes.

Infection with Trypanosoma cruzi produces a condition known as Chagas disease which affects at least 17 million people. Adenylate kinases, so called myokinases, are involved in a wide variety of processes, mainly related to their role in nucleotide interconversion and energy management. Recently, nuclear isoforms have been described in several organisms. This “atypical” isoform in terms of primary structure was associated to ribosomes biogenesis in yeast and to Cajal body organization in humans. Moreover nuclear adenylate kinases are essential for maintaining cellular homeostasis. In this manuscript we characterized T. cruzi nuclear adenylate kinase (TcADKn). TcADKn localizes in the nucleolus or cell cytoplasm. Nuclear shuttling mechanisms were also studied for the first time, being dependent on nutrient availability, oxidative stress and by the equivalent of the mammalian TOR pathway in T. cruzi. Furthermore we characterized the signals involved in nuclear importation and exportation processes. In addition, TcADKn expression levels are regulated at an mRNA level, being its 3′UTR involved in this process. These findings are the first steps in the understanding of ribosome processing in trypanosomatids.

Cloning, overexpression and characterization of Leishmania donovani triosephosphate isomerase

Triosephosphate isomerase (TIM) is a major enzyme in the glycolytic pathway, which catalyzes the interconversion of glyceraldehyde 3-phosphate to dihydroxyacetone phosphate. Here, we report cloning, expression and purification of a catalytically active recombinant TIM of Leishmania donovani (LdTIM). The recombinant LdTIM had a pH optimum in the range of 7.2-9.0, found stable at 25°C for 30 min and K(m) and V(max) for the substrate glyceraldehyde 3-phosphate was 0.328±0.02mM and 10.05mM/min/mg, respectively. The cysteine-reactive agent methylmethane thiosulphonate (MMTS) was used as probe, in order to test its effect on enzyme activity. The MMTS induced 75% enzyme inactivation within 15 min at 250 μM concentration. The biochemical characterization of LdTIM described in this work is the essential step towards deeper understanding of its role in parasite survival. The purification of LdTIM in bioactive form provides important tools for further functional and structural studies.

Singular features of trypanosomatids' phosphotransferases involved in cell energy management

Trypanosomatids are responsible for economically important veterinary affections and severe human diseases. In Africa, Trypanosoma brucei causes sleeping sickness or African trypanosomiasis, while in America, Trypanosoma cruzi is the etiological agent of Chagas disease. These parasites have complex life cycles which involve a wide variety of environments with very different compositions, physicochemical properties, and availability of metabolites. As the environment changes there is a need to maintain the nucleoside homeostasis, requiring a quick and regulated response. Most of the enzymes required for energy management are phosphotransferases. These enzymes present a nitrogenous group or a phosphate as acceptors, and the most clear examples are arginine kinase, nucleoside diphosphate kinase, and adenylate kinase. Trypanosoma and Leishmania have the largest number of phosphotransferase isoforms ever found in a single cell; some of them are absent in mammals, suggesting that these enzymes are required in many cellular compartments associated to different biological processes. The presence of such number of phosphotransferases support the hypothesis of the existence of an intracellular enzymatic phosphotransfer network that communicates the spatially separated intracellular ATP consumption and production processes. All these unique features make phosphotransferases a promising start point for rational drug design for the treatment of human trypanosomiasis.

Protein network prediction and topological analysis in Leishmania major as a tool for drug target selection

Background

Leishmaniasis is a virulent parasitic infection that causes a worldwide disease burden. Most treatments have toxic side-effects and efficacy has decreased due to the emergence of resistant strains. The outlook is worsened by the absence of promising drug targets for this disease. We have taken a computational approach to the detection of new drug targets, which may become an effective strategy for the discovery of new drugs for this tropical disease.

Results

We have predicted the protein interaction network of Leishmania major by using three validated methods: PSIMAP, PEIMAP, and iPfam. Combining the results from these methods, we calculated a high confidence network (confidence score > 0.70) with 1,366 nodes and 33,861 interactions. We were able to predict the biological process for 263 interacting proteins by doing enrichment analysis of the clusters detected. Analyzing the topology of the network with metrics such as connectivity and betweenness centrality, we detected 142 potential drug targets after homology filtering with the human proteome. Further experiments can be done to validate these targets.

Conclusion

We have constructed the first protein interaction network of the Leishmania major parasite by using a computational approach. The topological analysis of the protein network enabled us to identify a set of candidate proteins that may be both (1) essential for parasite survival and (2) without human orthologs. These potential targets are promising for further experimental validation. This strategy, if validated, may augment established drug discovery methodologies, for this and possibly other tropical diseases, with a relatively low additional investment of time and resources.

Crystal structure and functional analysis identify the P-loop containing protein YFH7 of Saccharomyces cerevisiae as an ATP-dependent kinase

Genome sequencing projects have revealed that P-loop proteins are highly represented in all organisms and that many of them have no attributed function. They are characterized by a conserved nucleotide-binding domain and carry different activities implicated in many cellular processes. Saccharomyces cerevisiae YFH7 is one of these P-loop proteins of unknown function. In this work we tried to integrate bioinformatics, structure, and enzymology to discover the function of YFH7. Sequence analysis revealed that yeast YFH7 is a yeast-specific protein showing weak similarity with the phosphoribulokinase/uridine kinase/bacterial pantothenate kinase (PRK/URK/PANK) subfamily of P-loop containing kinases. A large insertion of about 100 residues distinguishes YFH7 from other members of the family. The 1.95 A resolution crystal structure of YFH7 solved using the SAD method confirmed that YFH7 has a fold similar to the PRK/URK/PANK family, with the characteristic core, lid, and NMP(bind) domains. An additional alpha/beta domain of novel topology corresponds to the large sequence insertion. Structural and ligand binding analysis combined with enzymatic assays suggest that YFH7 is an ATP-dependent small molecule kinase with new substrate specificity.

Molecular cloning and biochemical characterization of Leishmania donovani serine hydroxymethyltransferase

Serine hydroxymethyltransferase (SHMT) catalyzes the inter conversion of serine and tetrahydrofolate (H(4)-folate) to form glycine and 5,10-methylene H(4)-folate and generates one-carbon fragments for the synthesis of nucleotides, methionine, thymidylate, choline, etc. In spite of being an indispensable enzyme of the thymidylate cycle, SHMT in Leishmania donovani remains uncharacterized. The study of L. donovani SHMT (ldSHMT) becomes important as this gene is preferentially expressed in the amastigote stage of parasite, which resides in human macrophages. Here we report cloning, expression and purification of a catalytically active ldSHMT. The homogeneity of recombinant protein was analyzed by denaturing gel electrophoresis and protein was found to be 95% pure having yield of 1mg/l. The recombinant protein is a tetramer of 216kDa as evidenced by gel filtration chromatography and uses serine and tetrahydrofolate as substrates with Km of 1.6 and 2.4mM, respectively. Further biochemical studies revealed that pH optimum of ldSHMT is 7.8 and enzyme is thermally stable up to 45 degrees C. ldSHMT was found sensitive towards denaturants as manifested by loss of enzyme activity at the concentration of 1M urea or 0.25M guanidine hydrochloride. This is the first report of purification and characterization of recombinant SHMT from any protozoan source. Studies on recombinant ldSHMT will help in evaluating this enzyme as potential drug target.

Adenylate Kinases 1 and 2 Are Part of the Accessory Structures in the Mouse Sperm Flagellum1

Proper sperm function depends on adequate ATP levels. In the mammalian flagellum, ATP is generated in the midpiece by oxidative respiration and in the principal piece by glycolysis. In locations where ATP is rapidly utilized or produced, adenylate kinases (AKs) maintain a constant adenylate energy charge by interconverting stoichiometric amounts of ATP and AMP with two ADP molecules. We previously identified adenylate kinase 1 and 2 (AK1 and AK2) by mass spectrometry as part of a mouse SDS-insoluble flagellar preparation containing the accessory structures (fibrous sheath, outer dense fibers, and mitochondrial sheath). A germ cell-specific cDNA encoding AK1 was characterized and found to contain a truncated 3' UTR and a different 5' UTR compared to the somatic Ak1 mRNA; however, it encoded an identical protein. Ak1 mRNA was upregulated during late spermiogenesis, a time when the flagellum is being assembled. AK1 was first seen in condensing spermatids and was associated with the outer microtubular doublets and outer dense fibers of sperm. This localization would allow the interconversion of ATP and ADP between the fibrous sheath where ATP is produced by glycolysis and the axonemal dynein ATPases where ATP is consumed. Ak2 mRNA was expressed at relatively low levels throughout spermatogenesis, and the protein was localized to the mitochondrial sheath in the sperm midpiece. AK1 and AK2 in the flagellar accessory structures provide a mechanism to buffer the adenylate energy charge for sperm motility.

A novel nuclear-localized protein with special adenylate kinase properties from Caenorhabditis elegans

The adrenal gland protein AD-004 like protein (ADLP) from Caenorhabditis elegans was cloned and expressed in Escherichia coli. Enzyme assays showed that ADLP has special adenylate kinase (AK) properties, with ATP and dATP as the preferred phosphate donors. In contrast to all other AK isoforms, AMP and dAMP were the preferred substrates of ADLP; CMP, TMP and shikimate acid were also good substrates. Subcellular localization studies showed a predominant nuclear localization for this protein, which is different from AK1-AK5, but similar to that of human AK6. These results suggest that ADLP is more likely a member of the AK6 family. Furthermore, RNAi experiments targeting ADLP were conducted and showed that RNAi treatment resulted in the suppression of worm growth.

Pathogenomics analysis of Leishmania spp.: flagellar gene families of putative virulence factors

The trypanosomatid flagellar apparatus contains conventional and unique features, whose roles in infectivity are still enigmatic. Although the flagellum and the flagellar pocket are critical organelles responsible for all vesicular trafficking between the cytoplasm and cell surface, still very little is known about their roles in pathogenesis and how molecules get to and from the flagellar pocket. The ongoing analysis of the genome sequences and proteome profiles of Leishmania major and L infantum, Trypanosoma cruzi, T. brucei, and T. gambiensi ( www.genedb.org ), coupled with our own work on L. chagasi (as part of the Brazilian Northeast Genome Program- www.progene.ufpe.br ), prompted us to scrutinize flagellar genes and proteins of Leishmania spp. promastigotes that could be virulence factors in leishmaniasis. We have identified some overlooked parasite factors such as the MNUDC-1 (a protein involved in nuclear development and genomic fusion) and SQS (an enzyme of sterol biosynthesis), among the described flagellar gene families. A database concerning the results of this work, as well as of other studies of Leishmania and its organelles, is available at http://nugen.lcc.uece.br/LPGate . It will serve as a convenient bioinformatics resource on genomics and pathology of the etiological agents of leishmaniasis.

Transactivating effect of complete S protein of hepatitis B virus and cloning of genes transactivated by complete S protein using suppression subtractive hybridization technique

AIM: To investigate the transactivating effect of complete S protein of hepatitis B virus (HBV) and to construct a subtractive cDNA library of genes transactivated by complete S protein of HBV by suppression subtractive hybridization (SSH) technique and to clone genes associated with its transactivation activity, and to pave the way for elucidating the pathogenesis of hepatitis B virus infection.

METHODS: pcDNA3.1(-)-complete S containing full-length HBV S gene was constructed by insertion of HBV complete S gene into BamH I/Kpn I sites. HepG2 cells were cotransfected with pcDNA3.1(-)-complete S and pSV-lacZ. After 48 h, cells were collected and detected for the expression of β-galactosidase (β-gal). Suppression subtractive hybridization and bioinformatics techniques were used. The mRNA of HepG2 cells transfected with pcDNA3.1(-)-complete S and pcDNA3.1(-) empty vector was isolated, and detected for the expression of complete S protein by reverse transcription polymerase chain reaction (RT-PCR) method, and cDNA was synthesized. After digestion with restriction enzyme RsaI, cDNA fragments were obtained. Tester cDNA was then divided into two groups and ligated to the specific adaptors 1 and 2, respectively. After tester cDNA had been hybridized with driver cDNA twice and underwent nested PCR twice, amplified cDNA fragments were subcloned into pGEM-Teasy vectors to set up the subtractive library. Amplification of the library was carried out within E. coli strain DH5α. The cDNA was sequenced and analyzed in GenBank with BLAST search after polymerase chain reaction (PCR) amplification.

RESULTS: The complete S mRNA could be detected by RT-PCR in HepG2 cells transfected with the pcDNA3.1(-)-complete S. The activity of β-gal in HepG2 cells transfected with the pcDNA3.1(-)-complete S was 6.9 times higher than that of control plasmid. The subtractive library of genes transactivated by HBV complete S protein was constructed successfully. The amplified library contains 86 positive clones. Colony PCR showed that 86 clones contained DNA inserts of 200-1 000 bp, respectively. Sequence analysis was performed in 35 clones randomly, and the full length sequences were obtained with bioinformatics method and searched for homologous DNA sequence from GenBank, altogether 33 coding sequences were obtained. These cDNA sequences might be target genes transactivated by complete S protein of HBV. Moreover, two unknown genes were discovered, full length coding sequences were obtained by bioinformatics techniques, one of them was named complete S transactivated protein 1 (CSTP1) and registered in GenBank (AY553877).

CONCLUSION: The complete S gene of HBV has a transactivating effect on SV40 early promoter. A subtractive cDNA library of genes transactivated by HBV complete S protein using SSH technique has been constructed successfully. The obtained sequences may be target genes transactivated by HBV complete S protein among which some genes coding proteins are involved in cell cycle regulation, metabolism, immunity, signal transduction, cell apoptosis and formation mechanism of hepatic carcinoma.

Expression, purification, and characterization of Leishmania donovani trypanothione reductase in Escherichia coli

Trypanothione reductase (TR) is an NADPH-dependent flavoprotein oxidoreductase central to thiol metabolism in all the trypanosomatids including Leishmania. The unique presence of this enzyme in trypanosomatids and absence in mammalian host make this enzyme an attractive target for the development of the antileishmanials. Complete open reading frame encoding trypanothione reductase from Leishmania donovani (Dd8 strain, causative agent of Indian visceral leishmaniasis) was cloned, sequenced, and expressed in Escherichia coli strain BL21 (DE3) as glutathione S-transferase fusion protein. The conditions were developed for overexpression of fusion protein in soluble form and purification of the recombinant protein to homogeneity. The recombinant LdTR was 54.68 kDa in size, dimeric in nature, and reduces oxidized trypanothione to reduced form. The kinetic parameters for trypanothione disulfide are K(m), 50 microM; k(cat), 18,181 min(-1); and k(cat)/K(m), 6.06x10(6) M(-1) s(-1). The yield of recombinant LdTR was approximately 16 mg/L bacterial culture and accounted for 6% of the total soluble proteins. The expressed protein was inhibited by known TR inhibitors as well as by SbIII, the known antileishmanial compound. This is the first report of large-scale production of any leishmanial TR in E. coli.