Expression, Purification, and Refolding of Active Recombinant Human E-selectin Lectin and EGF Domains in Escherichia coli

Molecular characterization of a fungal cyclophilin allergen Rhi o 2 and elucidation of antigenic determinants responsible for IgE-cross-reactivity

Cyclophilins are structurally conserved pan-allergens showing extensive cross-reactivity. So far, no precise information on cross-reactive IgE-epitopes of cyclophilins is available. Here, an 18-kDa IgE-reactive cyclophilin (Rhi o 2) was purified from Rhizopus oryzae, an indoor mold causing allergic sensitization. Based on LC-MS/MS-derived sequences of natural Rhi o 2, the full-length cDNA was cloned, and expressed as recombinant (r) allergen. Purified rRhi o 2 displayed IgE-reactivity and basophil degranulation with sera from all cyclophilin-positive patients. The melting curve of properly folded rRhi o 2 showed partial refolding after heat denaturation. The allergen displayed monomeric functional peptidyl-prolyl cis-trans isomerase (PPIase) activity. In IgE-inhibition assays, rRhi o 2 exhibited extensive cross-reactivity with various other cyclophilins reported as allergens from diverse sources including its homologous human autoantigen. By generating a series of deletion mutants, a conserved 69-residue (Asn⁸¹-Asn¹⁴⁹) fragment at C terminus of Rhi o 2 was identified as crucial for IgE-recognition and cross-reactivity. Grafting of the Asn⁸¹-Asn¹⁴⁹ fragment within the primary structure of yeast cyclophilin CPR1 by replacing its homologous sequence resulted in a hybrid molecule with structural folds similar to Rhi o 2. The IgE-reactivity and allergenic activity of the hybrid cyclophilin were greater than that of CPR1. Therefore, the Asn⁸¹-Asn¹⁴⁹ fragment can be considered as the site of IgE recognition of Rhi o 2. Hence, Rhi o 2 serves as a candidate antigen for the molecular diagnosis of mold allergy, and determination of a major cross-reactive IgE-epitope has clinical potential for the design of next-generation immunotherapeutics against cyclophilin-induced allergies.

Expression of Lectins in Heterologous Systems

Lectins are proteins that have the ability to recognize and bind in a reversible and specific way to free carbohydrates or glycoconjugates of cell membranes. For these reasons, they have been extensively used in a wide range of industrial and pharmacological applications. Currently, there is great interest in their production on a large scale. Unfortunately, conventional techniques do not provide the appropriate platform for this purpose and therefore, the heterologous production of lectins in different organisms has become the preferred method in many cases. Such systems have the advantage of providing better yields as well as more homogeneous and better-defined properties for the resultant products. However, an inappropriate choice of the expression system can cause important structural alterations that have repercussions on their biological activity since the specificity may lay in their post-translational processing, which depends largely on the producing organism. The present review aims to examine the most representative studies in the area, exposing the four most frequently used systems (bacteria, yeasts, plants and animal cells), with the intention of providing the necessary information to determine the strategy to follow in each case as well as their respective advantages and disadvantages.

High-yield reactivation of anionic tobacco peroxidase overexpressed in Escherichia coli

Anionic tobacco peroxidase (TOP) is extremely active in chemiluminescence reaction of luminol oxidation without addition of enhancers and more stable than horseradish peroxidase under antibody conjugation conditions. In addition, recombinant TOP (rTOP) produced in Escherichia coli is known to be a perfect direct electron transfer catalyst on electrodes of various origin. These features make the task of development of a high-yield reactivation protocol for rTOP practically important. Previous attempts to reactivate the enzyme from E. coli inclusion bodies were successful, but the reported reactivation yield was only 14%. In this work, we thoroughly screened the refolding conditions for dilution protocol and compared it with gel-filtration chromatography. The impressive reactivation yield in the dilution protocol (85%) was achieved for 8 μg/mL solubilized rTOP protein and the refolding medium containing 0.3 mM oxidized glutathione, 0.05 mM dithiothreitol, 5 mM CaCl2, 5% glycerol in 50 mM Tris-HCl buffer, pH 9.6, with 1 μM hemin added at the 24th hour of incubation. A practically important discovery was a 30-40% increase in the reactivation yield upon delayed addition of hemin. The reactivation yield achieved is one of the highest reported in the literature on protein refolding by dilution. The final yield of purified active non-glycosylated rTOP was ca. 60 mg per L of E. coli culture, close to the yield reported before for tomato and tobacco plants overexpressing glycosylated TOP (60 mg/kg biomass) and much higher than for the previously reported refolding protocol (2.6 mg per L of E. coli culture).