Mass spectrometric analysis of multiple pertussis toxins and toxoids

Development and validation of capillary electrophoresis sodium dodecyl sulfate (CE-SDS) method for purity analysis of pertussis toxin, filamentous haemagglutinin and pertactin antigens

We report here the development and validation of CE-SDS method for purity analysis of Acellular Pertussis vaccine components viz. purified Pertussis toxin (PTx), purified Filamentous haemagglutinin (FHA), and Pertactinantigen (PRN). The method was found to be specific and showed excellent linearity at a concentration range of 15.62 µg/mL-1000 µg/mL for purified PTx, 31.25 µg/mL-1000 µg/mL for purified FHA, and 3.9 µg/mL-1000 µg/mL for PRN antigen. Method reported limit of quantification (LOQ) 31.25 µg/mL, 62.5 µg/mL, and 7.8 µg/mL for purified PTx, FHA, and PRN respectively. Method precision (repeatability and intermediate precision) for purity and molecular weight determination in product matrix was below 10% for all three proteins. Method comparability studies were performed with SDS-PAGE. CE-SDS demonstrated corroborating results with SDS-PAGE for the estimation of purity and molecular weight analysis. However, CE-SDS method exhibited better resolution capabilities for resolving all the sub-unit peaks of PTx and isoforms of purified FHA. CE-SDS method also demonstrated stability indicating potential and thus fits its intended purpose as an effective analytical tool for quality control of acellular pertussis-based vaccines.

Trypanosoma rangeli protein tyrosine phosphatase is associated with the parasite's flagellum

Protein tyrosine phosphatases (PTPs) play an essential role in the regulation of cell differentiation in pathogenic trypanosomatids. In this study, we describe a PTP expressed by the non-pathogenic protozoan Trypanosoma rangeli (TrPTP2). The gene for this PTP is orthologous to the T. brucei TbPTP1 and Trypanosoma cruzi (TcPTP2) genes. Cloning and expression of the TrPTP2 and TcPTP2 proteins allowed anti-PTP2 monoclonal antibodies to be generated in BALB/c mice. When expressed by T. rangeli epimastigotes and trypomastigotes, native TrPTP2 is detected as a ~65 kDa protein associated with the parasite's flagellum. Given that the flagellum is an important structure for cell differentiation in trypanosomatids, the presence of a protein responsible for tyrosine dephosphorylation in the T. rangeli flagellum could represent an interesting mechanism of regulation in this structure.

A rapid method for capture and identification of immunogenic proteins in Bordetella pertussis enriched membranes fractions: a fast-track strategy applicable to other microorganisms

Mass spectrometry (MS) coupled with 1-D and 2-D electrophoresis can be utilized to detect and identify immunogenic proteins, but these methods are laborious and time-consuming. We describe an alternative, simple, rapid gel-free strategy to identify multiple immunogenic proteins from Bordetella pertussis (Bp). It couples immunoprecipitation to nano liquid chromatography- tandem mass spectrometry (IP-nLC-MS/MS) and is significantly both time- and labor-saving. We developed a gel-free magnetic bead-based immunoprecipitation (IP) method using different NP-40/PBS concentrations in which solubilized proteins of Bp Tohama I membrane fractions were precipitated with polyclonal rabbit anti-Bp whole cell immune sera. Immune complexes were analyzed by MS and Scaffold analysis (>95% protein identification probability). Total immunoproteins identified were 50, 63 and 49 for 0.90%, 0.45% and 0.22% NP-40/PBS buffer concentrations respectively. Known Bp proteins identified included pertactin, serotype 2 fimbrial subunit and filamentous hemagglutinin. As proof of concept that this gel-free protein immunoprecipitation method enabled the capture of multiple immunogenic proteins, IP samples were also analyzed by SDS-PAGE and immunoblotting. Bypassing gels and subjecting immunoprecipitated proteins directly to MS is a simple and rapid antigen identification method with relatively high throughput. IP-nLC-MS/MS provides a novel alternative approach for current methods used for the identification of immunogenic proteins.

Top-down proteomic identification of furin-cleaved α-subunit of Shiga toxin 2 from Escherichia coli O157:H7 using MALDI-TOF-TOF-MS/MS

A method has been developed to identify the α-subunit of Shiga toxin 2 (α-Stx2) from Escherichia coli O157:H7 using matrix-assisted laser desorption/ionization time-of-flight-time-of-flight tandem mass spectrometry (MALDI-TOF-TOF-MS/MS) and top-down proteomics using web-based software developed in-house. Expression of Stx2 was induced by culturing E. coli O157:H7 on solid agar supplemented with an antibiotic that elicits the bacterial SOS-response. Bacterial cell lysates were incubated in the presence of furin, a human enzyme, that cleaves α-Stx2 into A1 (~28 kDa) and A2 (~5 kDa) protein fragments. A subsequent disulfide reduction step unlinked A1 from A2. MALDI-TOF-MS of the furin-digested/disulfide-reduced sample showed a peak at mass-to-charge (m/z) 5286 that corresponded to the A2 fragment. No peak was observed that corresponded to the A1 fragment although its presence was confirmed by bottom-up proteomics. The peak at m/z 5286 was definitively identified by MALDI-TOF-TOF-MS/MS and top-down proteomics as the A2 fragment of α-Stx2.

Cloning and Expression of S1 Subunit of Pertussis Toxin in Escherichia coli

Bordetella pertussis is a gram negative bacterium that causes respiratory tract infection in human (whooping cough). Pertussis toxin (PT) is the main component of current acellular pertussis vaccine and the S1 (subunit1) is the main immunogenic part of it. Thus, S1 has been the target of many studies as a potent candidate of acellular vaccine against Bordetella pertussis, lacking the side effects of whole cell based ones. S1 gene was amplified and inserted in three expression vectors including pET-14b, pET-22b(+) and pAED4. The possibility and level of expression of these constructs were investigated in BL21 (DE3) strain of Escherichia coli (E.coli) as expression host. The highest expression was in pET-22b(+)-S1. Best expression achieved 6 hr post induction with 0.2 mM IPTG in LB broth containing ampicillin, at 30°C with shaking (250 rpm). Recombinant S1 protein was observed in two distinct separated proteins with 28 and 31 kDa estimated molecular weight. In spite of toxicity of PT and S1 in the E.coli, considerable amount of S1 was expressed in E.coli. Two rS1 bands were detected on SDS-PAGE. Both were confirmed as S1 in western blot with specific monoclonal and polyclonal antibodies against pertussis toxin. Appearance of two distinct bands could be the result of leader peptidase activity or nonspecific peptidase from E.coli on recombinant S1. As the recombinant S1 is a suitable antigen for studies as a candidate acellular vaccine or development of ELISA for detection of Bordetella pertussis, further studies are underway.