Construction, expression, and characterization of a recombinant annexin B1-low molecular weight urokinase chimera in Escherichia coli

Expression of the Tpanxb1 gene from Taenia pisiformis and its potential diagnostic value by dot-ELISA

Cysticercosis, caused by the larvae of Taenia pisiformis, is a common disease in rabbits that results in economic losses. To date, there has been limited information available on the early detection of infection by this parasite. This study describes a dot-ELISA method based on an autologous antigen annexin B1 (Tpanxb1). Its potential for serodiagnosis of rabbit cysticercosis was also evaluated. Western blot analysis revealed that the recombinant Tpanxb1 (rTpanxb1) protein could be specifically recognized by rabbit anti-sera. In serum trials, the antibodies could be detected by dot-ELISA using rTpanxb1 at 14 days post-infection. The positive response was present for up to 49 days post-infection. Based on the necropsy results of 169 rabbit samples, the relative sensitivity and specificity of the dot-ELISA were 94.55% and 92.86%, respectively. This study provides a foundation for studying the immunological function of annexin and its application to control Taenia cestodes.

Expression, purification, and characterization of a novel Ca(2+)- and phospholipid-binding protein annexin B2

Annexin B2 (AnxB2) is a novel member of the annexin family of Ca²⁺- and phospholipid-binding proteins from Cysticercus cellulosae. To obtain highly pure AnxB2 with an easy and inexpensive purification approach, its cDNA was cloned into the prokaryotic expression vector pJLA503 and the translation initiation codon was immediately under the control of the inducible bacteriophage λ promoters P_R and P_L. After induction by shifting temperature, large amounts of non-fusion protein were produced in Escherichia coli in a soluble form. Then a novel purification method based on Ca²⁺-dependent phosphatidylserine (PS)-binding activity was established, whereby the purity of AnxB2 was increased to 98.7%. Western blot analysis showed that recombinant AnxB2 was specifically recognized by serum of pigs infected with cysticercosis. In vitro test showed that, the recombinant AnxB2 had anticoagulant activity and platelet binding activity. The expression, purification, and initial characterization of AnxB2 set an important stage for further characterization of the protein.

Screening, purification, and identification of annexin B1 mutants with high phosphatidylserine-binding activity and reduced immunogenicity

Annexin B1 has many potential biomedical applications based on its high affinity for negatively charged phospholipid (phosphatidylserine, PS) in the presence of physiological concentrations of calcium. Low immunogenicity is prerequisite for the in vivo application of a nonhuman protein as a novel-imaging agent. In the present study, three sequence-deleted mutants with different numbers of functional domains were designed and expressed according to the predicted three-dimensional structure of annexin B1. The mutants of annexin B1, as well as the wild-type annexin B1, were expressed as Glutathione-S-transferase (GST)-fusion proteins. Two mutants with their purity above 80% could be obtained after one-step primary purification procedure on basis of the PS-binding activity. The immunogenicity of the two mutants was evaluated in mice by detecting the titers of elicited antigen-specific IgG. A member of three mutants of annexin B1, M12, which involved N-terminal amino-acid sequence and double functional domain I and II of annexin B1, was finally selected to detect apoptosis that is due to its lowest immunogenicity among the candidate mutants. Flourescein isothiocyanate-labeled M12 could bind the outer membranes of apoptotic cells and discriminate apoptotic cells in the early stage from necrotic cells when used with propidium iodide. (99m)Tc-labeled M12 could recognize the apoptotic hepatocytes induced by anti-Fas antibody treatment. Our data in vitro and in vivo demonstrated that M12 could be applied as a promising agent for the detection of apoptosis.

Expression and one-step purification of recombinant Arabidopsis thaliana frataxin homolog (AtFH)

Frataxin, a nuclear-encoded mitochondrial protein, has been proposed to participate in Fe-S cluster assembly, mitochondrial energy metabolism, respiration, and iron homeostasis. However, its precise function remains elusive. Frataxin is highly conserved in living organisms with no major structural changes, in particular at the C-terminal protein domain, suggesting that it plays a key function in all organisms. Recently, a plant gene, AtFH, with significant homology to other members of the frataxin family has been described. To gain insight on the frataxin role in plants, the frataxin domain was expressed in Escherichia coli BL21-codonPlus (DE3)-RIL cells and purified using a Ni-chelating column. The purified protein, added to a mixture containing Fe(II) and H2O2, attenuates the Fenton reaction indicating that the recombinant plant frataxin is functional. The procedure described here produced high yield of 99% pure protein through only one chromatographic step, suitable for further structure-function studies.