Enhancement of Solubility and Specific Activity of a Cu/Zn Superoxide Dismutase by Co-expression with a Copper Chaperone in Escherichia coli

Role of charged residues of the "electrostatic loop" of hSOD1 in promotion of aggregation: Implications for the mechanism of ALS-associated mutations under amyloidogenic conditions

Protein misfolding and amyloid formation are hallmarks of numerous diseases, including amyotrophic lateral sclerosis (ALS), in which hSOD1 aggregation is involved in pathogenesis. We used two point mutations in the electrostatic loop, G138E and T137R, to analyze charge distribution under destabilizing circumstances to gain more about how ALS-linked mutations affect SOD1 protein stability or net repulsive charge. We show that protein charge is important in the ALS disease process using bioinformatics and experiments. The MD simulation findings demonstrate that the mutant protein differs significantly from WT SOD1, which is consistent with the experimental evidence. The specific activity of the wild type was 1.61 and 1.48 times higher than that of the G138E and T137R mutants, respectively. Under amyloid induction conditions, the intensity of intrinsic and ANS fluorescence in both mutants reduced. Increasing the content of β-sheet structures in mutants can be attributed to aggregation propensity, which was confirmed using CD polarimetry and FTIR spectroscopy. Our findings show that two ALS-related mutations promote the formation of amyloid-like aggregates at near physiological pH under destabilizing conditions, which were detected using spectroscopic probes such as Congo red and ThT fluorescence, and also further confirmation of amyloid-like species by TEM. Overall, our results provide evidence supporting the notion that negative charge changes combined with other destabilizing factors play an important role in increasing protein aggregation by reducing repulsive negative charges.

A double point mutation of SOD1 targeting net charge promotes aggregation under destabilizing conditions: Correlation of charge distribution and ALS-provoking mutation

A progressive neurodegenerative illness such as amyotrophic lateral sclerosis (ALS) is characterized by the misfolding and aggregation of human CuZn superoxide dismutase (hSOD1) into amyloid aggregates. Thus, designing strategies for the choice of WT-SOD1 and double mutant (G12D/G138E) with an increased net negative charge can be a good idea to elucidate the pathological mechanism of SOD1 in ALS under some destabilizing conditions. Consequently, we show evidence that protein charge, together with other destabilizing conditions, plays an important role in ALS disease. To achieve this purpose, we use methods, such as spectroscopy and transmission electron microscopy (TEM) to monitor the formation of amyloid aggregation. The specific activity of WT-SOD1 was approximately 1.72 times higher than that of the double mutant. Under amyloidogenic circumstances, structural properties such as local, secondary, oligomeric, and fibrillar structures were explored. The double mutant's far-UV CD spectra displayed a broad minimum peak in the region 213 to 218 nm, suggesting the production of β-rich amyloid fibrils. FTIR spectra of the double mutant samples at different incubation times showed a low-frequency peak around 1630-1640 cm^-1, attributed to a parallel β-sheet. Moreover, CR-binding assay and TEM analysis revealed and confirmed that mutation with an increased repulsive charge promotes the formation of fibrous aggregates. Consequently, ALS mutations with a higher repulsive charge are the apparent exceptions that validate the rule. This findings revealed that the double mutant increases protein aggregation through a novel mechanism, likely involving destabilization of structure and a change in the net negative charge.

Cytoplasmic Chaperones Enhance Soluble Expression of Anti-EGFR huscFv in Escherichia coli

Background:

Overexpression of EGFR is associated with carcinogenesis in more than 70% of head and neck cancers. Anti-EGFR monoclonal antibodies bind to the extracellular domain of EGFR and block the EGFR downstream signaling pathway, which results in the suppression of the growth of the tumor cells. Escherichia coli is the preferred system for expressing various recombinant proteins, including single chain antibodies, but the formation of inclusion bodies negatively affects the efficacy of this system. Several strategies have been suggested to solve this problem, notably the utilization of molecular chaperones.

Objectives:

In this study, we attempted to increase the soluble expression of huscfv antibody via co-expression with the cytoplasmic chaperones.

Materials and Methods:

To achieve this purpose, chaperones plasmids pG-KJE8, pGro7, pKjE7, pTf16 and pG-Tf2 encoding cytoplasmic chaperones were co-expressed with the humanized anti-EGFR scFv construct in E. coli. Different temperatures, incubations times, and concentrations of IPTG were used to produce an active antibody with the highest solubility. Results were analyzed by SDS-PAGE. Soluble huscFv was purified by Ni-NTA column and the biologic activity of the recombinant protein was determined by ELISA.

Result:

The results indicated that the highest concentrations of humanized anti-EGFR scFv were obtained by co-expression of huscFv via chaperone plasmid pG-KJE8 with 0.2 mM concentration of inducer (IPTG), culture temperature of 25 °C, and 4 h incubation time after induction.

Conclusion:

In conclusion, co-expression with chaperones could be used as an efficient strategy to produce soluble active ScFvs in E. coli.

Antarctic marine ciliates under stress: superoxide dismutases from the psychrophilic Euplotes focardii are cold-active yet heat tolerant enzymes

Oxidative stress is a particularly severe threat to Antarctic marine polar organisms because they are exposed to high dissolved oxygen and to intense UV radiation. This paper reports the features of three superoxide dismutases from the Antarctic psychrophilic ciliate Euplotes focardii that faces two environmental challenges, oxidative stress and low temperature. Two out of these are Cu,Zn superoxide dismutases (named Ef-SOD1a and Ef-SOD1b) and one belongs to the Mn-containing group (Ef-SOD2). Ef-SOD1s and Ef-SOD2 differ in their evolutionary history, expression and overall structural features. Ef-SOD1 genes are expressed at different levels, with Ef-SOD1b mRNA 20-fold higher at the ciliate optimal temperature of growth (4 °C). All Ef-SOD enzymes are active at 4 °C, consistent with the definition of cold-adapted enzymes. At the same time, they display temperatures of melting in the range 50-70 °C and retain residual activity after incubation at 65-75 °C. Supported by data of molecular dynamics simulation, we conclude that the E. focardii SODs combine cold activity, local molecular flexibility and thermo tolerance.