Refolding of recombinant homodimeric malate dehydrogenase expressed in Escherichia coli as inclusion bodies

Cell-penetrable nanobodies (transbodies) that inhibit the tyrosine kinase activity of EGFR leading to the impediment of human lung adenocarcinoma cell motility and survival

Most patients suffering from non-small cell lung cancer (NSCLC) have epidermal growth factor receptor (EGFR) overexpression. Currently, EGFR tyrosine kinase inhibitors (TKIs) that act as the ATP-analogs and monoclonal antibodies (MAbs) to EGFR-ectodomain that block intracellular signaling are used for the treatment of advanced NSCLC. Unfortunately, adverse effects due to the TKI off-target and drug resistance occur in a significant number of the treated patients while some NSCLC genotypes do not respond to the therapeutic MAbs. Thus, a more effective remedy for the treatment of EGFR-overexpressed cancers is deemed necessary. In this study, VH/V_H H displayed-phage clones that are bound to recombinant EGFR-TK were fished-out from a humanized-camel VH/V_H H phage display library. VH/V_H H of three phage-infected Escherichia coli clones (VH18, V_H H35, and VH36) were linked molecularly to nonaarginine (R9) for making them cell penetrable. R9-VH18, R9-V_H H35, and R9-VH36 were cytotoxic to human adenocarcinomic alveolar basal epithelial cells (A549) at the fifty percent inhibitory concentration (IC₅₀ ) 0.181 ± 0.132, 0.00961 ± 0.00516, and 0.00996 ± 0.00752 μM, respectively, which were approximately 1000-fold more effective than small molecular TKIs. R9-VH18 and R9-VH36 also delayed cancer cell migration in a scratch-wound assay. Computerized homology modeling and intermolecular docking revealed that VH18 and V_H H35 used CDR3 to interact with EGFR-TK residues close to the catalytic site, which might sterically hinder the ATP-binding of the TK; VH36 used CDR2 to bind at the asymmetric dimerization surface, which might disrupt EGFR dimerization leading to inhibition of intracellular signaling. The humanized-cell penetrable nanobodies have a high potential for developing further towards a clinical application.

Refolding and purification of histidine-tagged protein by artificial chaperone-assisted metal affinity chromatography

This article has proposed an artificial chaperone-assisted immobilized metal affinity chromatography (AC-IMAC) for on-column refolding and purification of histidine-tagged proteins. Hexahistidine-tagged enhanced green fluorescent protein (EGFP) was overexpressed in Escherichia coli, and refolded and purified from urea-solubilized inclusion bodies by the strategy. The artificial chaperone system was composed of cetyltrimethylammonium bromide (CTAB) and beta-cyclodextrin (beta-CD). In the refolding process, denatured protein was mixed with CTAB to form a protein-CTAB complex. The mixture was then loaded to IMAC column and the complex was bound via metal chelating to the histidine tag. This was followed by washing with a refolding buffer containing beta-CD that removed CTAB from the bound protein and initiated on-column refolding. The effect of the washing time (i.e., on-column refolding time) on mass and fluorescence recoveries was examined. Extensive studies by comparison with other related refolding techniques have proved the advantages of AC-IMAC. In the on-column refolding, the artificial chaperone system suppressed protein interactions and facilitated protein folding to its native structure. So, the on-column refolding by AC-IMAC led to 99% pure EGFP with a fluorescence recovery of 80%. By comparison at a similar final EGFP concentration (0.6-0.8 mg/mL), this fluorescence recovery value was not only much higher than direct dilution (14%) and AC-assisted refolding (26%) in bulk solutions, but also superior to its partner, IMAC (60%). The operating conditions would be further optimized to improve the refolding efficiency.