Expression and copper binding studies of a Plasmodium falciparum protein with Cox19 copper binding motifs.

Copper can exist in an oxidized and a reduced form, which enables the metal to play essential roles as a catalytic co-factor in redox reactions in many organisms. Copper confers redox activity to the terminal electron transport chain cytochrome c oxidase protein. Cytochrome c oxidase in yeast obtains copper for the CuB site in the Cox1 subunit from Cox11 in association with Cox19. When copper is chelated in growth medium, Plasmodium falciparum parasite development in infected red blood cells is inhibited and excess copper is toxic for the parasite. The gene of a 26 kDa Plasmodium falciparum PfCox19 protein with two Cx9C Cox19 copper binding motifs, was cloned and expressed as a 66 kDa fusion protein with maltose binding protein and affinity purified (rMBP-PfCox19). rMBP-PfCox19 bound copper measured by: a bicinchoninic acid release assay; an in vivo bacterial host growth inhibition assay; ascorbate oxidation inhibition and differential scanning fluorimetry. The native protein was detected by antibodies raised against rMBP-PfCox19. PfCox19 binds copper and is predicted to associate with PfCox11 in the insertion of copper into the CuB site of Plasmodium cytochrome c oxidase. Characterisation of the proteins involved in Plasmodium spp. copper metabolism will help us understand the role of cytochrome c oxidase and this essential metal in Plasmodium homeostasis.

Expression and copper binding characteristics of Plasmodium falciparum cytochrome c oxidase assembly factor 11, Cox11.

BACKGROUND: Copper is an essential metal for living organisms as a catalytic co-factor for important enzymes, like cytochrome c oxidase the final enzyme in the electron transport chain. Plasmodium falciparum parasites in infected red blood cells are killed by excess copper and development in erythrocytes is inhibited by copper chelators. Cytochrome c oxidase in yeast obtains copper for the CuB site in the Cox1 subunit from Cox11. METHODS: A 162 amino acid carboxy-terminal domain of the P. falciparum Cox11 ortholog (PfCox11Ct) was recombinantly expressed and the rMBPPfCox11Ct affinity purified. Copper binding was measured in vitro and in Escherichia coli host cells. Site directed mutagenesis was used to identify key copper binding cysteines. Antibodies confirmed the expression of the native protein. RESULTS: rMBPPfCox11Ct was expressed as a 62 kDa protein fused with the maltose binding protein and affinity purified. rMBPPfCox11Ct bound copper measured by: a bicinchoninic acid release assay; atomic absorption spectroscopy; a bacterial host growth inhibition assay; ascorbate oxidation inhibition and in a thermal shift assay. The cysteine 157 amino acid was shown to be important for in vitro copper binding by PfCox11whilst Cys 60 was not. The native protein was detected by antibodies against rMBPPfCox11Ct. CONCLUSIONS: Plasmodium spp. express the PfCox11 protein which shares structural features and copper binding motifs with Cox11 from other species. PfCox11 binds copper and is, therefore, predicted to transfer copper to the CuB site of Plasmodium cytochrome c oxidase. Characterization of Plasmodium spp. proteins involved in copper metabolism will help sceintists understand the role of cytochrome c oxidase and this essential metal in Plasmodium homeostasis.

Crystal violet stains proteins in SDS-PAGE gels and zymograms.

Coomassie brilliant blue R250, an anionic dye is the most popular stain to detect proteins resolved in SDS-PAGE gels. Crystal violet, a cationic dye was found to be versatile and stained proteins in SDS-PAGE gels and in zymograms. Stained proteins can be transferred to nitrocellulose and the stained proteins on the western detected with enzyme coupled antibodies. Staining can be reversed. Staining takes 3 h at RT or 30 min at 60 °C. Crystal violet stained some E. coli high and low molecular weight proteins not stained by Coomassie blue R250. Crystal violet stained down to 16 ng of protein, some five-fold lower than Coomassie blue, though the two stains had a similar linear dynamic range. The staining sensitivity could be increased to 2 ng when crystal violet and Coomassie blue were combined in a double staining/counterion dye formulation. The low concentrations of the dye without a destaining step reduces the costs of the technique and results in a more environmentally friendly stain compared to traditional staining methods.

Improving diagnostic performance of 18F-FDG-PET/CT for assessment of regional nodal involvement in non-small cell lung cancer.

AIM: To assess the diagnostic performance of combined 2-[18F]-fluoro-2-deoxy-d-glucose (18F-FDG) positron-emission tomography (PET)/computed tomography (CT) mediastinal blood pool (MBP) activity cut-off for staging nodal involvement, and to examine other variables that may improve the diagnostic performance of PET/CT in non-small cell lung cancer (NSCLC). MATERIALS AND METHODS: All patients diagnosed with NSCLC who underwent endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) and 18F-FDG-PET/CT between June 2016 and August 2018 were included. Nodal station and nodal staging-based analyses were performed, comparing the MBP cut-off and five other PET/CT parameters (node maximum standardised uptake value [SUVmax], node/MBP SUVmax ratio, node/tumour SUVmax ratio, node short axis diameter, and node SUVmax/node short axis diameter ratio) with histopathology results. The optimal cut-off value for each PET/CT parameter was determined using receiver operating characteristic curve analysis. RESULTS: One hundred and thirteen patients with a total of 321 nodes with pathological sampling were included. Nodal activity above MBP on PET/CT demonstrated 97.4% sensitivity, 35.8% specificity, 32.8% positive predictive value, and 97.8% negative predictive value. Of the five other PET/CT parameters examined, the two most promising were node SUVmax and node/MBP SUVmax. The node SUVmax cut-off of 3.9 demonstrated 90.9% sensitivity and 61.9% specificity, and the node/MBP SUVmax cut-off of 1.7 demonstrated 90.9% sensitivity and 60.7% specificity. CONCLUSION: Compared to the MBP cut-off, use of a higher node/MBP SUVmax ratio cut-off and use of other PET/CT variables can improve the diagnostic performance of PET/CT for NSCLC nodal staging. In particular, specificity for detecting malignant nodal involvement is improved while maintaining high sensitivity.

Monocyte phagocytosis of malaria ß-haematin in the presence of artemisinin, amodiaquine, chloroquine, doxycycline, primaquine, pyrimethamine and quinine.

The intraerythrocytic malaria parasite digests haemoglobin to provide amino acids for metabolism and releases toxic haem that is sequestered into haemozoin, a non-toxic, insoluble, crystalline pigment. Following erythrocyte rupture, haemozoin is released into circulation and phagocytosed by monocytes. Phagocytosed haemozoin and antimalarial drugs have both been reported to modulate monocyte functions. This study determined the effects of therapeutic concentrations of seven antimalarial drugs; amodiaquine, artemisinin, chloroquine, doxycycline, primaquine, pyrimethamine and quinine, on the phagocytosis of ß-haematin (synthetic haemozoin) by two monocytic cell lines, J774A.1 and U937, and human peripheral blood mononuclear cells. A novel spectrophotometric method based on the absorbance (O.D 400 nm) of alkali/SDS treated monocytes containing ß-haematin was developed to complement counting phagocytosis with microscopy. The method has potential use for the large scale screening of monocyte phagocytic activity. Artemisinin, quinine, primaquine and pyrimethamine activated ß-haematin phagocytosis by 12% or more, whereas amodiaquine, chloroquine and doxycyline inhibited ß-haematin phagocytosis. In contrast, antimalarial drugs had minimal inhibitory effects on the phagocytosis of latex beads with only quinine resulting in more than 20% inhibition. Antimalarial drugs appear to alter monocyte phagocytic activity which has implications for the treatment, pathogenicity and adjunct therapies for malaria.

Towards development of aptamers that specifically bind to lactate dehydrogenase of Plasmodium falciparum through epitopic targeting.

BACKGROUND: Early detection is crucial for the effective treatment of malaria, particularly in those cases infected with Plasmodium falciparum. There is a need for diagnostic devices with the capacity to distinguish P. falciparum from other strains of malaria. Here, aptamers generated against targeted species-specific epitopes of P. falciparum lactate dehydrogenase (rPfLDH) are described. RESULTS: Two classes of aptamers bearing high binding affinity and specificity for recombinant P. falciparum lactate dehydrogenase (rPfLDH) and P. falciparum-specific lactate dehydrogenase epitopic oligopeptide (LDHp) were separately generated. Structurally-relevant moieties with particular consensus sequences (GGTAG and GGCG) were found in aptamers reported here and previously published, confirming their importance in recognition of the target, while novel moieties particular to this work (ATTAT and poly-A stretches) were identified. Aptamers with diagnostically-supportive functions were synthesized, prime examples of which are the aptamers designated as LDHp 1, LDHp 11 and rLDH 4 and rLDH 15 in work presented herein. Of the sampled aptamers raised against the recombinant protein, rLDH 4 showed the highest binding to the target rPfLDH in the ELONA assay, with both rLDH 4 and rLDH 15 indicating an ability to discriminate between rPfLDH and rPvLDH. LDHp 11 was generated against a peptide selected as a unique P. falciparum LDH peptide. The aptamer, LDHp 11, like antibodies against the same peptide, only detected rPfLDH and discriminated between rPfLDH and rPvLDH. This was supported by affinity binding experiments where only aptamers generated against a unique species-specific epitope showed an ability to preferentially bind to rPfLDH relative to rPvLDH rather than those generated against the whole recombinant protein. In addition, rLDH 4 and LDHp 11 demonstrated in situ binding to P. falciparum cells during confocal microscopy. CONCLUSIONS: The utilization and application of LDHp 11, an aptamer generated against a unique species-specific epitope of P. falciparum LDH indicated the ability to discriminate between recombinant P. falciparum and Plasmodium vivax LDH. This aptamer holds promise as a biorecognition element in malaria diagnostic devices for the detection, and differentiation, of P. falciparum and P. vivax malaria infections. This study paves the way to explore aptamer generation against targeted species-specific epitopes of other Plasmodium species.

Plasmodium glyceraldehyde-3-phosphate dehydrogenase: A potential malaria diagnostic target.

Malaria rapid diagnostic tests (RDTs) are immunochromatographic tests detecting Plasmodial histidine-rich protein 2 (HRP2), lactate dehydrogenase (LDH) and aldolase. HRP2 is only expressed by Plasmodium falciparum parasites and the protein is not expressed in several geographic isolates. LDH-based tests lack sensitivity compared to HRP2 tests. This study explored the potential of the Plasmodial glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), as a new malaria diagnostic biomarker. The P. falciparum and P. yoelii proteins were recombinantly expressed in BL21(DE3) Escherischia coli host cells and affinity purified. Two epitopes (CADGFLLIGEKKVSVFA and CAEKDPSQIPWGKCQV) specific to P. falciparum GAPDH and one common to all mammalian malaria species (CKDDTPIYVMGINH) were identified. Antibodies were raised in chickens against the two recombinant proteins and the three epitopes and affinity purified. The antibodies detected the native protein in parasite lysates as a 38 kDa protein and immunofluorescence verified a parasite cytosolic localization for the native protein. The antibodies suggested a 4-6 fold higher concentration of native PfGAPDH compared to PfLDH in immunoprecipitation and ELISA formats, consistent with published proteomic data. PfGAPDH shows interesting potential as a malaria diagnostic biomarker.

Comparing Antibody Responses in Chickens Against Plasmodium falciparum Lactate Dehydrogenase and Glyceraldehyde-3-phosphate Dehydrogenase with Freund's and Pheroid® Adjuvants.

Pheroid® technology was assessed as an alternative to Freund's adjuvant to raise antibodies in experimental animals. Chickens were immunized with two recombinantly expressed Plasmodium falciparum proteins, lactate dehydrogenase (PfLDH) and glyceraldehyde-3-phosphate dehydrogenase (PfGAPDH), alone or in combination with Freund's adjuvant or Pheroid®. Chicken egg yolk antibodies (IgY) were isolated and compared for specificity, sensitivity and yield. Freund's adjuvant and Pheroid® stimulated prolonged antibody responses in chickens against both antigens. Affinity purified antibodies had specificity for the recombinant and the native proteins on Western blots. Antibodies generated in the presence of Freund's adjuvant had high sensitivity for both antigens. Pheroid® generated antibodies that detected the lowest concentration of recombinant PfLDH. Freund's adjuvant and Pheroid® both improved chicken IgY yields, with Pheroid® showing a 2-fold increase relative to controls. Pheroid® was well-tolerated in chickens and has potential for development as a safe adjuvant for testing alternative stimulatory factors to improve adjuvant formulations.

Identification and initial characterisation of a Plasmodium falciparum Cox17 copper metallochaperone.

Copper is an essential micronutrient for all living organisms as an important catalytic co-factor for key enzymes. In higher eukaryotes intracellular copper is distributed by copper metallochaperones. Copper chelators such as neocuproine and tetrathiomolybdate inhibit Plasmodium falciparum erythrocytic development, indicating a requirement for copper by the parasite. A screen of the P. falciparum genome database identified eight potential copper-requiring protein orthologs, including four candidate copper metallochaperones implicated in the delivery of copper to cytochrome-c oxidase. A P. falciparum Cox17 ortholog (PfCox17) was recombinantly expressed and the purified protein bound reduced copper in vitro. PfCox17 was localised to the parasite cytoplasm. Characterisation of plasmodial proteins involved in copper metabolism will help us understand the role of this essential microelement in plasmodial homeostasis.

A Plasmodium falciparum copper-binding membrane protein with copper transport motifs.

BACKGROUND: Copper is an essential catalytic co-factor for metabolically important cellular enzymes, such as cytochrome-c oxidase. Eukaryotic cells acquire copper through a copper transport protein and distribute intracellular copper using molecular chaperones. The copper chelator, neocuproine, inhibits Plasmodium falciparum ring-to-trophozoite transition in vitro, indicating a copper requirement for malaria parasite development. How the malaria parasite acquires or secretes copper still remains to be fully elucidated. METHODS: PlasmoDB was searched for sequences corresponding to candidate P. falciparum copper-requiring proteins. The amino terminal domain of a putative P. falciparum copper transport protein was cloned and expressed as a maltose binding fusion protein. The copper binding ability of this protein was examined. Copper transport protein-specific anti-peptide antibodies were generated in chickens and used to establish native protein localization in P. falciparum parasites by immunofluorescence microscopy. RESULTS: Six P. falciparum copper-requiring protein orthologs and a candidate P. falciparum copper transport protein (PF14_0369), containing characteristic copper transport protein features, were identified in PlasmoDB. The recombinant amino terminal domain of the transport protein bound reduced copper in vitro and within Escherichia coli cells during recombinant expression. Immunolocalization studies tracked the copper binding protein translocating from the erythrocyte plasma membrane in early ring stage to a parasite membrane as the parasites developed to schizonts. The protein appears to be a PEXEL-negative membrane protein. CONCLUSION: Plasmodium falciparum parasites express a native protein with copper transporter characteristics that binds copper in vitro. Localization of the protein to the erythrocyte and parasite plasma membranes could provide a mechanism for the delivery of novel anti-malarial compounds.

Summary of the British Thoracic Society guidelines for advanced diagnostic and therapeutic flexible bronchoscopy in adults.

This new guideline covers the rapidly advancing field of interventional bronchoscopy using flexible bronchoscopy. It includes the use of more complex diagnostic procedures such as endobronchial ultrasound, interventions for the relief of central airway obstruction due to malignancy and the recent development of endobronchial therapies for chronic obstructive pulmonary disease and asthma. The guideline aims to help all those who undertake flexible bronchoscopy to understand more about this important area. It also aims to inform respiratory physicians and other specialists dealing with lung cancer of the procedures possible in the management and palliation of central airway obstruction. The guideline covers transbronchial needle aspiration and endobronchial ultrasound-guided transbronchial needle aspiration, electrocautery/diathermy, argon plasma coagulation and thermal laser, cryotherapy, cryoextraction, photodynamic therapy, brachytherapy, tracheobronchial stenting, electromagnetic navigation bronchoscopy, endobronchial valves for emphysema and bronchial thermoplasty for asthma.

Predictive accuracy of patient-reported exacerbation frequency in COPD.

Chronic obstructive pulmonary disease (COPD) exacerbation frequency is important for clinical risk assessment and trial recruitment. In order to accurately establish exacerbation frequency, patients need to be followed for 1 yr, although this is not always practical. 1) Patient recall of exacerbation number during the year prior to recruitment to the London COPD cohort was compared with the number of exacerbations recorded on diary cards during the subsequent year; and 2) patient recall of their exacerbation number after 1 yr of follow-up was compared with documented exacerbations over the same year. A total of 267 patients (forced expiratory volume in 1 s 1.14 L) recorded worsening of respiratory symptoms on daily diary cards for 1 yr. Exacerbations were defined according to previously validated criteria. There was no difference between the exacerbation number recalled by patients prior to recruitment and the number detected during the first year (median 2.0 (interquartile range 1.0-4.0) and 2.0 (1.0-4.0); expected agreement 76.4%; agreement 84.6%; κ = 0.3469). There was no difference between the number of exacerbations remembered by patients and the number recorded on diary cards over the same 1-yr period (2.0 (1.0-4.0) for both groups; expected agreement 74.9%; actual agreement 93.3%; κ = 0.6146). Patients remember the number of exacerbations they have in a year. Accuracy is increased when comparing the same 1-yr period. Patient recall is sufficiently robust for stratification into frequent and infrequent exacerbator groups for subsequent years.

Plasmodium falciparum: effect of antimalarial drugs, malaria pigment (ß-haematin) and Plasmodium falciparum lysate on monocyte GTP-cyclohydrolase 1 gene expression.

In interferon-γ activated human macrophages, GTP-cyclohydrolase 1 catalyses the conversion of guanosine triphosphate to 7,8-dihydroneopterin triphosphate, which is dephosphorylated and oxidized to form neopterin. Elevated levels of neopterin have been detected in the urine and serum of malaria-infected patients. In this study, U937 cells were treated with interferon-γ and one of the following antimalarial drugs: amodiaquine, artemisinin, chloroquine, doxycycline, primaquine, pyrimethamine or quinine. The effects of treating the U937 cells with malaria pigment (ß-haematin), latex beads, or Plasmodium falciparum-infected-red blood cell lysates were also investigated. U937 GTP-cyclohydrolase 1 mRNA expression was monitored using reverse-transcriptase-quantitative PCR. Artemisinin, primaquine, and quinine down-regulated GTP-cyclohydrolase 1 gene expression 1.26-, 1.29-, and 1.63-fold, respectively. The remaining drugs had insignificant effects. ß-haematin up-regulated GTP-cyclohydrolase 1 mRNA expression 1.18-fold, whereas P. falciparum-infected red blood cell lysate down-regulated expression 1.56-fold. These results show the differing immunomodulatory actions of antimalarial drugs and malaria pigment taking place in monocytes.

Direct red 81 and amido black stain proteins in polyacrylamide electrophoresis gels within 10 min.

Proteins separated by SDS-polyacrylamide gel electrophoresis can be stained with organic dyes, the most popular being Coomassie brilliant blue R-250. Coomassie R-250 staining of ovalbumin in an SDS-PAGE gel increased linearly from 2.5 to 60 min. Direct red 81 and amido black staining approached saturation in 10 min. Scatchard analysis showed that the number of direct red 81 and amido black ligands bound to ovalbumin was fourfold higher than that of Coomassie R-250. Direct red 81 and amido black stain proteins in an SDS-polyacrylamide electrophoresis gel in 10 min.

Isolation of Nile crocodile (Crocodylus niloticus) serum immunoglobulin M and Y (IgM and IgY).

Crocodile immunity has not been fully characterised with more studies on crocodile innate immunity than cell-mediated or humoral immunity. Crocodile immunoglobulin genes have been described but immunoglobulin proteins have not been isolated or studied biochemically. Two large proteins proposed to be crocodile IgM and IgY were isolated and purified from Crocodylus niloticus sera using two different protocols. A 50% (w/v) ammonium sulfate and a 15% (w/v) polyethylene glycol precipitation step was followed by Cibacron blue F3GA affinity- and Sephacryl-S300 gel filtration chromatography. An alternate purification protocol, with only two steps, involved thiophilic affinity- and Sephacryl-S300 gel filtration chromatography. The purified crocodile IgM resolved on reducing SDS-PAGE with an apparent mass of 180 kDa. Purified crocodile IgY resolved at 180 kDa alongside chicken IgY on a non-reducing SDS-PAGE gel, and is deduced to consist of two 66 kDa heavy and two 23 kDa light chains under reducing conditions. The thiophilic/gel filtration two-step protocol gave three-fold higher yields of isolated protein than the four-step precipitation/chromatography protocol. Antibodies against the isolated crocodile IgM and IgY were raised in chickens and affinity purified. The chicken antibodies differentiated between crocodile IgM and IgY and have the potential for use in the diagnosis of crocodile infections. The purified crocodile antibodies can be biochemically characterised and compared to mammalian and avian antibodies to give a better understanding of crocodile humoral immunity.

Expression and copper binding properties of the N-terminal domain of copper P-type ATPases of African trypanosomes.

Copper is an essential component of cuproproteins but can be toxic to cells, therefore copper metabolism is very carefully regulated within cells. To gain insight into trypanosome copper metabolism, Trypanosoma spp. genomic databases were screened for the presence of copper-containing and -transporting proteins. Among other genes encoding copper-binding proteins, a copper-transporting P-type ATPase (CuATPase) gene was identified. Sequence and phylogenetic analyses suggest that the gene codes for a Cu+ transporter belonging to the P1B-1 ATPase subfamily that has an N-terminal domain with copper binding motifs. The N-terminal cytosolic domains of the proteins from Trypanosoma congolense and Trypanosoma brucei brucei were recombinantly expressed in Escherichia coli as maltose binding protein (MBP) fusion proteins. These N-terminal domains bound copper in vitro and within E. coli cells, more than the control MBP fusion partner alone. The copper binding properties of the recombinant proteins were further confirmed when they inhibited copper catalysed ascorbate oxidation. Native CuATPases were detected in a western blot of lysates of T. congolense IL3000 and T. b. brucei ILTat1.1 bloodstream form parasites using affinity purified IgY antibodies against N-terminal domain peptides. The CuATPase was also detected by immunofluorescence in T. b. brucei bloodstream form parasites where it was associated with subcellular vesicles. In conclusion, Trypanosoma species express a copper-transporting P1B-1-type ATPase and together with other copper-binding proteins identified in the genomes of kinetoplastid parasites may constitute potential targets for anti-trypanosomal drug discovery.

Measuring Protein Concentration with Absorbance, Lowry, Bradford Coomassie Blue, or the Smith Bicinchoninic Acid Assay Before Electrophoresis.

Measuring the concentration of proteins is an essential part of enzyme analysis or serves to monitor protein yields and losses during protein isolation procedures. Decisions on the usefulness of any protein isolation procedure depend on knowing the concentration of proteins before and after a procedure. Protein concentration in solution is generally measured with spectrophotometry in the UV range or in the presence of dyes or copper interacting with the protein. This review describes absorbance at 280 nm, the Lowry, Bradford (Coomassie Blue), and Smith (bicinchoninic acid) assays for measuring protein and includes suggestions for optimizing each method.

Concentrating Proteins by Salt, Polyethylene Glycol, Solvent, SDS Precipitation, Three-Phase Partitioning, Dialysis, Centrifugation, Ultrafiltration, Lyophilization, Affinity Chromatography, Immunoprecipitation or Increased Temperature for Protein Isolation, Drug Interaction, and Proteomic and Peptidomic Evaluation.

In protein isolation, drug interaction studies, and proteomic or peptidomic procedures, protein solutions are often concentrated to remove solvents and undesirable molecules, to separate protein fractions, or to increase protein concentrations. Proteins can be concentrated by precipitation from solution with ammonium sulfate, polyethylene glycol, organic solvents, trichloroacetic acid, potassium chloride/sodium dodecyl sulfate thermal denaturation, and three-phase partitioning. Solvents can be removed by passage through a semipermeable barrier where protein solutions are forced against the barrier in a centrifuge tube or with increased pressure, concentrating proteins in the remaining solution. The semipermeable barrier can be surrounded by a hygroscopic reagent to draw the solvent across the membrane. Proteins can be concentrated by freeze-drying (lyophilization). Unique ligand interactions with proteins can be used to select for proteins by affinity purification or immunoprecipitation. All these methods to concentrate proteins are discussed.

Continuous Elution SDS-PAGE with a Modified Standard Gel Apparatus to Separate and Isolate an Array of Proteins from Complex Mixtures.

Sodium dodecyl sulfate polyacrylamide gel electrophoresis is a powerful tool to separate proteins according to their relative sizes. The technique provides information about both the size of a number of proteins and potentially the comparative amounts of each protein. To confirm the identity of proteins, proteins can be eluted from the gel and transferred electrophoretically to nitrocellulose for antibody-based detection. During electrophoresis, if the current is not stopped, proteins continue to pass down the gel and elute from the bottom of the gel. The standard electrophoresis gel apparatus can be employed with the addition of some tubing and alterations to the separating gel to collect proteins separated by size as they elute from the base of the gel as described in this chapter. Complex protein mixtures can be separated into multiple fractions containing single proteins in a few hours. Small amounts (<500 µg of protein) of protein sample can be fractionated.

Oligopeptidase B: a processing peptidase involved in pathogenesis.

Oligopeptidase B is a "processing peptidase" from the prolyl oligopeptidase family of serine peptidases present in Gram negative bacteria, protozoa and plants. Unlike the prototype prolyl oligopeptidase, oligopeptidase B hydrolyses peptides on the carboxyl side of pairs of basic amino acid residues. Molecular modelling and mutation studies have identified carboxyl dyads in the C-terminal catalytic domain that mediate substrate and inhibitor binding. The peptidase is efficiently inhibited by non-peptide irreversible serine peptidase inhibitors, peptidyl-chloromethylketones, -phosphonate alpha-aminoalkyl diphenyl esters with basic residues at P1, and tripeptide aldehydes, but not by proteinaceous host plasma inhibitors such as alpha2-macroglobulin and serpins. Access of these large molecular mass inhibitors and substrates larger than approximately 30 amino acid residues to the catalytic cleft is restricted by the N-terminal beta-propeller domain. The physiological role of oligopeptidase B from various sources has not yet been elucidated. However, the peptidase has been identified as an important virulence factor and therapeutic agent in animal trypanosomosis. This review highlights the structure-function properties of oligopeptidase B in context with its physiological and/or pathological roles which make the enzyme a promising drug target.