Purification of penicillin-binding protein 2 of Escherichia coli

Neospora caninum: functional inhibition of protein disulfide isomerase by the broad-spectrum anti-parasitic drug nitazoxanide and other thiazolides

Nitazoxanide (NTZ) and several NTZ-derivatives (thiazolides) have been shown to exhibit considerable anti-Neospora caninum tachyzoite activity in vitro. We coupled tizoxanide (TIZ), the deacetylated metabolite, to epoxy-agarose-resin and performed affinity chromatography with N. caninum tachyzoite extracts. Two main protein bands of 52 and 43kDa were isolated. The 52kDa protein was readily recognized by antibodies directed against NcPDI, and mass spectrometry confirmed its identity. Poly-histidine-tagged NcPDI-cDNA was expressed in Escherichia coli and recombinant NcPDI (recNcPDI) was purified by Co2+-affinity chromatography. By applying an enzyme assay based on the measurement of insulin crosslinking activity, recNcPDI exhibited properties reminiscent for PDIs, and its activity was impaired upon the addition of classical PDI inhibitors such as bacitracin (1-2mM), para-chloromercuribenzoic acid (0.1-1mM) and tocinoic acid (0.1-1mM). RecNcPDI-mediated insulin crosslinking was inhibited by NTZ (5-100 microM) in a dose-dependent manner. In addition, the enzymatic activity of recNcPDI was inhibited by those thiazolides that also affected parasite proliferation. Thus, thiazolides readily interfere with NcPDI, and possibly also with PDIs from other microorganisms susceptible to thiazolides.

A novel Giardia lamblia nitroreductase, GlNR1, interacts with nitazoxanide and other thiazolides

The nitrothiazole analogue nitazoxanide [NTZ; 2-acetolyloxy-N-(5-nitro-2-thiazolyl)benzamide] represents the parent compound of a class of drugs referred to as thiazolides and exhibits a broad spectrum of activities against a wide variety of helminths, protozoa, and enteric bacteria infecting animals and humans. NTZ and other thiazolides are active against a wide range of other intracellular and extracellular protozoan parasites in vitro and in vivo, but their mode of action and respective subcellular target(s) have only recently been investigated. In order to identify potential targets of NTZ and other thiazolides in Giardia lamblia trophozoites, we have developed an affinity chromatography system using the deacetylated derivative of NTZ, tizoxanide (TIZ), as a ligand. Affinity chromatography on TIZ-agarose using cell extracts of G. lamblia trophozoites resulted in the isolation of an approximately 35-kDa polypeptide, which was identified by mass spectrometry as a nitroreductase (NR) homologue (EAA43030.1). NR was overexpressed as a six-histidine-tagged recombinant protein in Escherichia coli, purified, and then characterized using an assay for oxygen-insensitive NRs with dinitrotoluene as a substrate. This demonstrated that the NR was functionally active, and the protein was designated GlNR1. In this assay system, NR activity was severely inhibited by NTZ and other thiazolides, demonstrating that the antigiardial activity of these drugs could be, at least partially, mediated through inhibition of GlNR1.

Nucleotide sequence of the pbpA gene and characteristics of the deduced amino acid sequence of penicillin-binding protein 2 of Escherichia coli K12

We have determined the nucleotide sequence of the pbpA gene encoding penicillin-binding protein (PBP) 2 of Escherichia coli. The coding region for PBP 2 was 1899 base pairs in length and was preceded by a possible promoter sequence and two open reading frames. The primary structure of PBP 2, deduced from the nucleotide sequence, comprised 633 amino acid residues. The relative molecular mass was calculated to be 70867. The deduced sequence agreed with the NH2-terminal sequence of PBP 2 purified from membranes, suggesting that PBP 2 has no signal peptide. The hydropathy profile suggested that the NH2-terminal hydrophobic region (a stretch of 25 non-ionic amino acids) may anchor PBP 2 in the cytoplasmic membrane as an ectoprotein. There were nine homologous segments in the amino acid sequence of PBP 2 when compared with PBP 3 of E. coli. The active-site serine residue of PBP 2 was predicted to be Ser-330. Around this putative active-site serine residue was found the conserved sequence of Ser-Xaa-Xaa-Lys, which has been identified in all of the other E. coli PBPs so far studied (PBPs 1A, 1B, 3, 5 and 6) and class A and class C beta-lactamases. In the higher-molecular-mass PBPs 1A, 1B, 2 and 3, Ser-Xaa-Xaa-Lys-Pro was conserved. In the putative peptidoglycan transpeptidase domain there were six amino acid residues, which are common only in the PBPs of higher molecular mass.

Antigenic relationships among penicillin-binding proteins 1 from members of the families Pasteurellaceae and Enterobacteriaceae

Penicillin-binding proteins (PBPs) from Haemophilus influenzae RD purified by a combination of affinity chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and electroelution were used to immunize rabbits to obtain specific antisera. Antisera directed against PBP 1 (1b) of H. influenzae cross-reacted with representative organisms of the family Pasteurellaceae and with many members of the family Enterobacteriaceae but not with other gram-negative organisms. Immunization with purified PBP 3 of H. influenzae produced antisera that reacted with PBP 1 (1b) of H. influenzae and showed the same cross-reactive pattern with other species as the anti-PBP 1 antiserum. A 24,000-molecular-weight polypeptide of H. influenzae, not radiolabeled by [35S]penicillin, reacted with antisera against purified PBPs 1 (1a, 1b), 2, and 3. The results suggest that antigenic epitopes are shared among similar PBPs from related species and even among different PBPs within the same species.