Expression in Escherichia coli, purification and kinetic characterization of LAPLm, a Leishmania major M17-aminopeptidase.

The Leishmania major leucyl-aminopeptidase (LAPLm), a member of the M17 family of proteases, is a potential drug target for treatment of leishmaniasis. To better characterize enzyme properties, recombinant LAPLm (rLAPLm) was expressed in Escherichia coli. A LAPLm gene was designed, codon-optimized for expression in E. coli, synthesized and cloned into the pET-15b vector. Production of rLAPLm in E. coli Lemo21(DE3), induced for 4 h at 37 °C with 400 µM IPTG and 250 µM l-rhamnose, yielded insoluble enzyme with a low proportion of soluble and active protein, only detected by an anti-His antibody-based western-blot. rLAPLm was purified in a single step by immobilized metal ion affinity chromatography. rLAPLm was obtained with a purity of ~10% and a volumetric yield of 2.5 mg per liter, sufficient for further characterization. The aminopeptidase exhibits optimal activity at pH 7.0 and a substrate preference for Leu-p-nitroanilide (appKM = 30 µM, appkcat = 14.7 s-1). Optimal temperature is 50 °C, and the enzyme is insensitive to 4 mM Co2+, Mg2+, Ca2+ and Ba2+. However, rLAPLm was activated by Zn2+, Mn2+ and Cd2+ but is insensitive towards the protease inhibitors PMSF, TLCK, E-64 and pepstatin A, being inhibited by EDTA and bestatin. Bestatin is a potent, non-competitive inhibitor of the enzyme with a Ki value of 994 nM. We suggest that rLAPLm is a suitable target for inhibitor identification.

Role of TRF2 and TPP1 regulation in idiopathic recurrent pregnancy loss.

Telomeres are the tandem repeats (TTAGGG) present at the ends of the chromosomes that ensure chromosome stability and protect chromosomes from degradation. Telomeres in somatic human cells shorten after every cellular division and are linked to the cellular senescence. In this study we have investigated telomere length and expression of shelterin genes in aborted fetus material from idiopathic recurrent pregnancy losses. Telomere length was measured using Telomere Restriction Fragment Length (TRF) analysis. The gene expression levels for important shelterin complex proteins (TRF1, TRF2, POT1, and TPP1) were determined by Real-time Quantitative Reverse Transcriptase PCR (qRT-PCR). Our results demonstrated down regulation of TRF2 and TPP1 and a strong decline in average telomere length in abort material from women suffering from idiopathic recurrent pregnancy loss. We suggest that shorter telomere length and downregulation of the major shelterin components TRF2 and TPP1 leading to "telomere uncapping", might play a critical role in recurrent pregnancy loss.

Enzymatic characterization of a novel Xaa-Pro aminopeptidase XpmA from Aspergillus oryzae expressed in Escherichia coli.

Xaa-Pro aminopeptidases are peptidases responsible for the cleavage of any amino acid N-terminally adjacent to a proline residue. We identified a gene encoding a putative Xaa-Pro aminopeptidase in the genome of the filamentous fungus Aspergillus oryzae (genome database number: AO090701000720) and named this gene xpmA. We produced its enzyme in a C-terminally His6-tag-fused form in an Escherichia coli expression system and purified it. The purified recombinant XpmA (rXpmA) showed hydrolysis activity toward Xaa-Pro-oligopeptides, especially the two dipeptides Ala-Pro and Phe-Pro. The molecular weight of rXpmA was estimated to be 69 kDa by SDS-PAGE and 126 kDa by gel filtration, suggesting that it is a homodimer. The enzyme was activated by various divalent metal ions such as Mn2+, Co2+, and Mg2+; in particular, the enzyme activity was increased 27.6-times relative to the no-addition control by 1 mM Mn2+. Additionally, 10 mM EDTA suppressed its activity to 0.26-times of the control level. Therefore, rXpmA was a metalloprotease. Optimal hydrolytic activity of rXpmA was observed at 50°C and pH 8.5-9.0. The enzyme was stable up to 50°C and from pH 4.0 to 11.0. rXpmA showed substrate inhibition by Leu-Pro, Ser-Pro and Arg-Pro at concentrations over 4 mM, 10 mM, and 3 mM, respectively. NaCl increased the enzyme activity in the concentration range 0.5-3.0 M, suggesting that the enzyme is halophilic.

XPNPEP2 is overexpressed in cervical cancer and promotes cervical cancer metastasis.

XPNPEP2 is a proline hydrolytic enzyme that hydrolyzes several biologically active peptides and causes a loss of substrate activity. However, its function in cancer is still unknown. Our study showed that XPNPEP2 expression was significantly upregulated in cervical cancer tissues compared with normal cervical tissues and cervical intraepithelial neoplasm tissues. Statistical analysis showed that XPNPEP2 expression was associated with the International Federation of Gynecology and Obstetrics stage and lymph node metastasis. Overexpression of XPNPEP2 in SiHa and HeLa cells promoted cell invasion and migration without affecting cell proliferation and apoptosis. Mechanistically, we found that XPNPEP2 facilitated cervical cancer cell invasion and migration by inducing epithelial-mesenchymal transition. Furthermore, we demonstrated that XPNPEP2 had significant effects on the metastasis of xenografted tumors in vivo. Collectively, our findings identify the novel function of XPNPEP2 in the metastasis of cervical cancer and suggest that XPNPEP2 could be a novel potential therapeutic target for the treatment of cervical cancer.

Enhanced lysosomal activity by overexpressed aminopeptidase Y in Saccharomyces cerevisiae.

Saccharomyces cerevisiae contains vacuoles corresponding to lysosomes in higher eukaryotes. Lysosomes are dynamic (not silent) organelles in which enzymes can be easily integrated or released when exposed to stressful conditions. Changes in lysosomal enzymes have been observed due to oxidative stress, resulting in an increased function of lysosomes. The protein profiles from H2O2- and NH4Cl-treated lysosomes showed different expression patterns, observed with two-dimensional gel electrophoresis. The aminopeptidase Y protein (APE3) that conspicuously enhanced antimicrobial activity than other proteins was selected for further studies. The S. cerevisiae APE3 gene was isolated and inserted into pYES2.0 expression vector. The GFP gene was inserted downstream to the APE3 gene for confirmation of APE3 targeting to lysosomes, and S. cerevisiae was transformed to pYES2::APE3::GFP. The APE3 did not enter in lysosomes and formed an inclusion body at 30 °C, but it inserted to lysosomes as shown by the merger of GFP with lysosomes at 28 °C. Antimicrobial activity of the cloned S. cerevisiae increased about 5 to 10 % against eight strains, compared to normal cells, and galactose induction is increased more two folds than that of normal cells. Therefore, S. cerevisiae was transformed to pYES2::APE3::GFP, accumulating a large amount of APE3, resulting in increased lysosomal activity. Increase in endogenous levels of lysosomes and their activity following genetic modification can lead to its use in applications such as antimicrobial agents and apoptosis-inducing materials for cancer cells, and consequently, it may also be possible to use the organelles for improving in vitro functions.

Biased expression, under the control of single promoter, of human interferon α-2b and Escherichia coli methionine amino peptidase genes in E. coli, irrespective of their distance from the promoter.

Human interferon α-2b and Escherichia coli methionine amino peptidase genes were cloned independently as well as bicistronically in expression plasmid pET-21a (+). Production of human interferon α-2b was comparable to that of E. coli methionine amino peptidase when these genes were expressed independently in E. coli BL21-CodonPlus (DE3)-RIL. However, human interferon α-2b was produced in a much less amount whereas there was no difference in the production of methionine amino peptidase when the encoding genes were expressed bicistronically. It is important to note that human interferon α-2b was the first gene in order, after the promoter and E. coli methionine amino peptidase was the next with a linker sequence of 27 nucleotides between them.

Altered Activity and Expression of Cytosolic Peptidases in Colorectal Cancer.

BACKGROUND AND OBJECTIVE: The role of peptidases in carcinogenic processes and their potential usefulness as tumor markers in colorectal cancer (CRC) have been classically attributed to cell-surface enzymes. The objective of the present study was to analyze the activity and mRNA expression of three cytosolic peptidases in the CRC and to correlate the obtained results with classic histopathological parameters for tumor prognosis and survival. METHODS: The activity and mRNA levels of puromycin-sensitive aminopeptidase (PSA), aminopeptidase B (APB) and pyroglutamyl-peptidase I (PGI) were measured by fluorimetric and quantitative RT-PCR methods in colorectal mucosa and tumor tissues and plasma samples from CRC patients (n=81). RESULTS: 1) PSA and APB activity was higher in adenomas and carcinomas than in the uninvolved mucosa. 2) mRNA levels of PSA and PGI was lower in tumors. 3) PGI activity in CRC tissue correlated negatively with histological grade, tumor size and 5-year overall survival of CRC patients. 4) Higher plasmatic APB activity was independently associated with better 5-year overall survival. CONCLUSIONS: Data suggest that cytosolic peptidases may be involved in colorectal carcinogenesis and point to the determination of this enzymes as a valuable method in the determination of CRC prognosis.

Ubenimex inhibits cell proliferation, migration and invasion in renal cell carcinoma: the effect is autophagy-associated.

Ubenimex is a low-molecular-weight dipeptide with the ability to inhibit aminopeptidase N (APN) activity, enhance the function of immunocompetent cells and confer antitumor effects. We sought to characterize the effects of ubenimex on renal cell carcinoma (RCC). The 786-O and OS-RC-2 human RCC cell lines were positive for APN expression and ubenimex decreased APN activity without affecting the expression. Ubenimex suppressed the proliferation of both cell lines in a concentration­dependent manner, as assessed by curve growth analysis and WST-8 proliferation assay. Wound healing and Matrigel invasion assays demonstrated that the migration and invasion of the RCC cells were also markedly suppressed by ubenimex. Furthermore, ubenimex increased the mortality of both RCC cell lines as determined by the LDH cytotoxicity assay. This affect was accompanied by increased levels of LC3B with no apparent effect on Caspase3; and we observed that autophagy increased significantly after ubenimex treatment in both RCC cell lines by electron microscopy. Moreover, rapamycin enhanced the cytotoxic effect of ubenimex, while 3-methyladenine reversed the effect, indicating that ubenimex cytotoxicity occured through an autophagy-related mechanism. To further assess the potential applicability of ubenimex in the treatment of RCC, we performed immunohistochemistry using tissue microarrays representing 76 RCC patients that underwent radical nephrectomy. The results showed that APN was expressed in most, but not all of the RCC tissues and that the expression was reduced in RCC as compared to the normal kidney tissues, suggesting a potential role for APN in RCC development. Collectively, these results indicated that ubenimex inhibits proliferation, migration and invasion of RCC cells. Ubenimex may induce autophagy, which may be associated with its effect on the growth arrest and the cell death of RCC cells.

Differences between disease-associated endoplasmic reticulum aminopeptidase 1 (ERAP1) isoforms in cellular expression, interactions with tumour necrosis factor receptor 1 (TNF-R1) and regulation by cytokines.

Endoplasmic reticulum aminopeptidase 1 (ERAP1) processes peptides for major histocompatibility complex (MHC) class I presentation and promotes cytokine receptor ectodomain shedding. These known functions of ERAP1 may explain its genetic association with several autoimmune inflammatory diseases. In this study, we identified four novel alternatively spliced variants of ERAP1 mRNA, designated as ΔExon-11, ΔExon-13, ΔExon-14 and ΔExon-15. We also observed a rapid and differential modulation of ERAP1 mRNA levels and spliced variants in different cell types pretreated with lipopolysaccharide (LPS). We have studied three full-length allelic forms of ERAP1 (R127-K528, P127-K528, P127-R528) and one spliced variant (ΔExon-11) and assessed their interactions with tumour necrosis factor receptor 1 (TNF-R1) in transfected cells. We observed variation in cellular expression of different ERAP1 isoforms, with R127-K528 being expressed at a much lower level. Furthermore, the cellular expression of full-length P127-K528 and ΔExon-11 spliced variant was enhanced significantly when co-transfected with TNF-R1. Isoforms P127-K528, P127-R528 and ΔExon-11 spliced variant associated with TNF-R1, and this interaction occurred in a region within the first 10 exons of ERAP1. Supernatant-derived vesicles from transfected cells contained the full-length and ectodomain form of soluble TNF-R1, as well as carrying the full-length ERAP1 isoforms. We observed marginal differences between TNF-R1 ectodomain levels when co-expressed with individual ERAP1 isoforms, and treatment of transfected cells with tumour necrosis factor (TNF), interleukin (IL)-1ß and IL-10 exerted variable effects on TNF-R1 ectodomain cleavage. Our data suggest that ERAP1 isoforms may exhibit differential biological properties and inflammatory mediators could play critical roles in modulating ERAP1 expression, leading to altered functional activities of this enzyme.

TPPII, MYBBP1A and CDK2 form a protein-protein interaction network.

Tripeptidyl-peptidase II (TPPII) is an aminopeptidase with suggested regulatory effects on cell cycle, apoptosis and senescence. A protein-protein interaction study revealed that TPPII physically interacts with the tumor suppressor MYBBP1A and the cell cycle regulator protein CDK2. Mutual protein-protein interaction was detected between MYBBP1A and CDK2 as well. In situ Proximity Ligation Assay (PLA) using HEK293 cells overexpressing TPPII forming highly enzymatically active oligomeric complexes showed that the cytoplasmic interaction frequency of TPPII with MYBBP1A increased with the protein expression of TPPII and using serum-free cell growth conditions. A specific reversible inhibitor of TPPII, butabindide, suppressed the cytoplasmic interactions of TPPII and MYBBP1A both in control HEK293 and the cells overexpressing murine TPPII. The interaction of MYBBP1A with CDK2 was confirmed by in situ PLA in two different mammalian cell lines. Functional link between TPPII and MYBBP1A has been verified by gene expression study during anoikis, where overexpression of TPP II decreased mRNA expression level of MYBBP1A at the cell detachment conditions. All three interacting proteins TPPII, MYBBP1A and CDK2 have been previously implicated in the research for development of tumor-suppressing agents. This is the first report presenting mutual protein-protein interaction network of these proteins.

Neuronal ceroid lipofuscinosis genes, CLN2, CLN3 and CLN5 are spatially and temporally co-expressed in a developing mouse brain.

Neuronal ceroid lipofuscinosis (NCL) diseases consist of a group of genetically inherited neurodegenerative disorders that share common symptoms such as seizures, psychomotor retardation, blindness, and premature death. Although gene defects behind the NCL diseases are well characterized, very little is known how these defects affect normal development of the brain and cause the pathology of the disease. To obtain understanding of the development of the cell types that are mostly affected by defective function of CLN proteins, timing of expression of CLN2, CLN3 and CLN5 genes was investigated in developing mouse brain. The relationship between the expression pattern and the developmental stage of the brain showed that these genes are co-expressed spatially and temporally during brain development. Throughout the development strong expression of the three mRNAs was detected in germinal epithelium and in ventricle regions, hippocampus and cerebellum, all representing regions that are known to be associated with the formation of new neurons. More specifically, RT-PCR studies on developing mouse cortices revealed that the CLN genes were temporally co-expressed in the neural progenitor cells together with known stem cell markers. This suggested that CLN2, CLN3 and CLN5 genes may play an important role in early embryonal neurogenesis.

High-level expression in Escherichia coli, purification and kinetic characterization of Plasmodium falciparum M1-aminopeptidase.

Plasmodium falciparum neutral metallo-aminopeptidase (PfAM1), a member of the M1 family of metallo proteases, is a promising target for malaria, a devastating human parasitic disease. We report the high-level expression of PfAM1 in Escherichia coli BL21. An optimized gene, with a codon adaptation index and an average G/C content higher than the native gene, was synthesized and cloned in the pTrcHis2B vector. Optimal expression was achieved by induction with 1mM IPTG at 37°C for 18h. This allowed obtaining 100mg of recombinant PfAM1 (rPfAM1) per L of culture medium; 19% of the E. coli soluble protein mass was from rPFAM1. rPfAM1, fused to an amino-terminal 6×His tag, was purified in a single step by immobilized metal ion affinity chromatography. The protein showed only limited signs of proteolytic degradation, and this step increased purity 27-fold. The kinetic characteristics of rPfAM1, such as a neutral optimal pH, a preference for substrates with basic or hydrophobic amino acids at the P1 position, an inhibition profile typical of metallo-aminopeptidases, and inhibition from Zn(2+) excess, were similar to those of the native PfAM1. We have thus optimized an expression system that should be useful for identifying new PfAM1 inhibitors.

p53 increases MHC class I expression by upregulating the endoplasmic reticulum aminopeptidase ERAP1.

The p53 tumour suppressor has an important role in cancer cells. Here we show that p53 regulates expression of major histocompatibility complex I on the cell surface. We show that the tumour cell line HCT116, which lacks p53 exhibits significantly lower major histocompatibility complex I expression than its wild-type counterpart. Using a combination of chromatin immunoprecipitation sequencing and gene expression analysis, we demonstrate that p53 upregulates expression of endoplasmic reticulum aminopeptidase 1 by binding to its cognate response element in the ERAP1 gene. Silencing of p53 decreases endoplasmic reticulum aminopeptidase 1 protein levels and therefore major histocompatibility complex I expression. We further show that this mechanism operates in A549 cells infected with H1N1 influenza virus, in which H1N1 activates p53, leading to endoplasmic reticulum aminopeptidase 1 upregulation and a corresponding increase in major histocompatibility complex I expression. Our study suggests a previously unrecognized link between p53 function and the immunosurveillance of cancer and infection.

Overexpression of peptide deformylase in breast, colon, and lung cancers.

BACKGROUND: Human mitochondrial peptide deformylase (PDF) has been proposed as a novel cancer therapeutic target. However, very little is known about its expression and regulation in human tissues. The purpose of this study was to characterize the expression pattern of PDF in cancerous tissues and to identify mechanisms that regulate its expression. METHODS: The mRNA expression levels of PDF and methionine aminopeptidase 1D (MAP1D), an enzyme involved in a related pathway with PDF, were determined using tissue panels containing cDNA from patients with various types of cancer (breast, colon, kidney, liver, lung, ovarian, prostate, or thyroid) and human cell lines. Protein levels of PDF were also determined in 2 colon cancer patients via western blotting. Colon cancer cells were treated with inhibitors of ERK, Akt, and mTOR signaling pathways and the resulting effects on PDF and MAP1D mRNA levels were determined by qPCR for colon and lung cancer cell lines. Finally, the effects of a PDF inhibitor, actinonin, on the proliferation of breast, colon, and prostate cell lines were determined using the CyQUANT assay. RESULTS: PDF and MAP1D mRNA levels were elevated in cancer cell lines compared to non-cancer lines. PDF mRNA levels were significantly increased in breast, colon, and lung cancer samples while MAP1D mRNA levels were increased in just colon cancers. The expression of PDF and MAP1D varied with stage in these cancers. Further, PDF protein expression was elevated in colon cancer tissue samples. Inhibition of the MEK/ERK, but not PI3K or mTOR, pathway reduced the expression of PDF and MAP1D in both colon and lung cancer cell lines. Further, inhibition of PDF with actinonin resulted in greater reduction of breast, colon, and prostate cancer cell proliferation than non-cancer cell lines. CONCLUSIONS: This is the first report showing that PDF is over-expressed in breast, colon, and lung cancers, and the first evidence that the MEK/ERK pathway plays a role in regulating the expression of PDF and MAP1D. The over-expression of PDF in several cancers and the inhibition of cancer cell growth by a PDF inhibitor suggest this enzyme may act as an oncogene to promote cancer cell proliferation.

Pyridinylquinazolines selectively inhibit human methionine aminopeptidase-1 in cells.

Methionine aminopeptidases (MetAPs), which remove the initiator methionine from nascent peptides, are essential in all organisms. While MetAP2 has been demonstrated to be a therapeutic target for inhibiting angiogenesis in mammals, MetAP1 seems to be vital for cell proliferation. Our earlier efforts identified two structural classes of human MetAP1 (HsMetAP1)-selective inhibitors (1-4), but all of them failed to inhibit cellular HsMetAP1. Using Mn(II) or Zn(II) to activate HsMetAP1, we found that 1-4 could only effectively inhibit purified HsMetAP1 in the presence of physiologically unachievable concentrations of Co(II). In an effort to seek Co(II)-independent inhibitors, a novel structural class containing a 2-(pyridin-2-yl)quinazoline core has been discovered. Many compounds in this class potently and selectively inhibited HsMetAP1 without Co(II). Subsequently, we demonstrated that 11j, an auxiliary metal-dependent inhibitor, effectively inhibited HsMetAP1 in primary cells. This is the first report that an HsMetAP1-selective inhibitor is effective against its target in cells.

Gemfibrozil and fenofibrate, Food and Drug Administration-approved lipid-lowering drugs, up-regulate tripeptidyl-peptidase 1 in brain cells via peroxisome proliferator-activated receptor α: implications for late infantile Batten disease therapy.

The classical late infantile neuronal ceroid lipofuscinosis (LINCLs) is an autosomal recessive disease, where the defective gene is Cln2, encoding tripeptidyl-peptidase I (TPP1). At the molecular level, LINCL is caused by accumulation of autofluorescent storage materials in neurons and other cell types. Currently, there is no established treatment for this fatal disease. This study reveals a novel use of gemfibrozil and fenofibrate, Food and Drug Administration-approved lipid-lowering drugs, in up-regulating TPP1 in brain cells. Both gemfibrozil and fenofibrate up-regulated mRNA, protein, and enzymatic activity of TPP1 in primary mouse neurons and astrocytes as well as human astrocytes and neuronal cells. Because gemfibrozil and fenofibrate are known to activate peroxisome proliferator-activated receptor-α (PPARα), the role of PPARα in gemfibrozil- and fenofibrate-mediated up-regulation of TPP1 was investigated revealing that both drugs up-regulated TPP1 mRNA, protein, and enzymatic activity both in vitro and in vivo in wild type (WT) and PPARß(-/-), but not PPARα(-/-), mice. In an attempt to delineate the mechanism of TPP1 up-regulation, it was found that the effects of the fibrate drugs were abrogated in the absence of retinoid X receptor-α (RXRα), a molecule known to form a heterodimer with PPARα. Accordingly, all-trans-retinoic acid, alone or together with gemfibrozil, up-regulated TPP1. Co-immunoprecipitation and ChIP studies revealed the formation of a PPARα/RXRα heterodimer and binding of the heterodimer to an RXR-binding site on the Cln2 promoter. Together, this study demonstrates a unique mechanism for the up-regulation of TPP1 by fibrate drugs via PPARα/RXRα pathway.

Synergistic activation of the pathogenicity-related proline iminopeptidase gene in Xanthomonas campestris pv. campestris by HrpX and a LuxR homolog.

Xanthomonas campestris pv. campestris strain 8004 contains an orphan quorum-sensing (QS) locus, xccR-pip(Xcc), in which the proline iminopeptidase (pip(Xcc)) gene (where "Xcc" indicates that the pip gene is from X. campestris pv. campestris) is positively regulated by the LuxR homologue XccR by binding to the luxXc box of the pip(Xcc) promoter. The disruption of pip(Xcc) significantly attenuated the virulence of X. campestris pv. campestris. An imperfect plant-inducible promoter (PIP) box is located in the upstream region of the pip(Xcc) promoter, which is the putative binding site of the transcriptional activator HrpX. To explore whether the expression of the pip(Xcc) gene is regulated by HrpX, the expression level of a pip(Xcc) promoter-gusA fusion gene was assayed in an hrpX disruption mutant. The results showed that the lack of HrpX dramatically decreased the ß-glucuronidase (GUS) activity. Further analyses using an electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP)-PCR indicated that the imperfect PIP box in X. campestris pv. campestris is specifically bound to HrpX. These data demonstrated that the pip(Xcc) gene belongs to the hrp regulon and that the imperfect PIP box of the pip(Xcc) promoter could be a cis element for the HrpX protein. We further showed in a pulldown assay that XccR can bind HrpX, suggesting that these two regulatory proteins coactivate the virulence factor by binding to the different cis elements of the pip(Xcc) gene and adapt to the host environment during X. campestris pv. campestris infection.

Biochemical characterization of recombinant methionine aminopeptidases (MAPs) from Mycobacterium tuberculosis H37Rv.

Methionine aminopeptidase (MAP) performs the essential post-translational N-terminal methionine excision (NME) of nascent polypeptides during protein synthesis. To characterize MAP from Mycobacterium tuberculosis, two homolgues, mapA (Rv0734) and mapB (Rv2861c), were over expressed and purified as recombinant proteins in E. coli. In vitro activity assay of apo-MtbMAPs using L-Met-p-nitro anilide as substrate revealed MtbMAP A to be catalytically more efficient compared to MtbMAP B. Ni(2+) was the best activator of apo-MtbMAP A, whereas Ni(2+) and Co(2+) activated apo-MtbMAP B equally. MtbMAP B showed higher thermo-stability, but was feedback inhibited by higher concentrations of L-methionine. Aminopeptidase inhibitors like actinonin and bestatin inhibited both MtbMAPs, more prominently MtbMAP B. Among the site-directed mutants of MtbMAP B, substitution of metal-binding residue D142 completely abolished enzyme activity, whereas substitution of residues forming S1' pocket, C105S and T94C, had only moderate effects on substrate hydrolysis. Present study identified a specific insertion region in MtbMAP A sequence which differentiates it from other bacterial and eukaryotic MAPs. A deletion mutant lacking amino acids from this insertion region (MtbMAP A-∆164-176) was constructed to probe into their structural and functional role in activity and stability of MtbMAP A. The limited success in soluble expression of this deletion mutant suggests further optimizations of expression conditions or alternative bioinformatics approaches for further characterization of this deletion mutant of MtbMAP A.

TsPAP1 encodes a novel plant prolyl aminopeptidase whose expression is induced in response to suboptimal growth conditions.

A triticale cDNA encoding a prolyl aminopeptidase (PAP) was obtained by RT-PCR and has been designated as TsPAP1. The cloned cDNA is 1387 bp long and encodes a protein of 390 amino acids with a calculated molecular mass of 43.9 kDa. The deduced TsPAP1 protein exhibits a considerable sequence identity with the biochemically characterized bacterial and fungal PAP proteins of small molecular masses (∼35 kDa). Moreover, the presence of conserved regions that are characteristic for bacterial monomeric PAP enzymes (the GGSWG motif, the localization of the catalytic triad residues and the segment involved in substrate binding) has also been noted. Primary structure analysis and phylogenetic analysis revealed that TsPAP1 encodes a novel plant PAP protein that is distinct from the multimeric proteins that have thus far been characterized in plants and whose counterparts have been recognized only in bacteria and fungi. A significant increase in the TsPAP1 transcript level in the shoots of triticale plants was observed under drought and saline conditions as well as in the presence of cadmium and aluminium ions in the nutrient medium. This paper is the first report describing changes in the transcript levels of any plant PAP in response to suboptimal growth conditions.

Exploring the active site of tripeptidyl-peptidase II through studies of pH dependence of reaction kinetics.

Tripeptidyl-peptidase II (TPP II) is a subtilisin-like serine protease which forms a large enzyme complex (>4MDa). It is considered a potential drug target due to its involvement in specific physiological processes. However, information is scarce concerning the kinetic characteristics of TPP II and its active site features, which are important for design of efficient inhibitors. To amend this, we probed the active site by determining the pH dependence of TPP II catalysis. Access to pure enzyme is a prerequisite for kinetic investigations and herein we introduce the first efficient purification system for heterologously expressed mammalian TPP II. The pH dependence of kinetic parameters for hydrolysis of two different chromogenic substrates, Ala-Ala-Phe-pNA and Ala-Ala-Ala-pNA, was determined for murine, human and Drosophila melanogaster TPP II as well as mutant variants thereof. The investigation demonstrated that TPP II, in contrast to subtilisin, has a bell-shaped pH dependence of k(cat)(app)/K(M) probably due to deprotonation of the N-terminal amino group of the substrate at higher pH. Since both the K(M) and k(cat)(app) are lower for cleavage of AAA-pNA than for AAF-pNA we propose that the former can bind non-productively to the active site of the enzyme, a phenomenon previously observed with some substrates for subtilisin. Two mutant variants, H267A and D387G, showed bell-shaped pH-dependence of k(cat)(app), possibly due to an impaired protonation of the leaving group. This work reveals previously unknown differences between TPP II orthologues and subtilisin as well as features that might be conserved within the entire family of subtilisin-like serine peptidases.