Protein folding, misfolding, and refolding of therapeutic proteins

N-Acetyl-Cysteine: Modulating the Cysteine Redox Proteome in Neurodegenerative Diseases

In the last twenty years, significant progress in understanding the pathophysiology of age-associated neurodegenerative diseases has been made. However, the prevention and treatment of these diseases remain without clinically significant therapeutic advancement. While we still hope for some potential genetic therapeutic approaches, the current reality is far from substantial progress. With this state of the issue, emphasis should be placed on early diagnosis and prompt intervention in patients with increased risk of neurodegenerative diseases to slow down their progression, poor prognosis, and decreasing quality of life. Accordingly, it is urgent to implement interventions addressing the psychosocial and biochemical disturbances we know are central in managing the evolution of these disorders. Genomic and proteomic studies have shown the high molecular intricacy in neurodegenerative diseases, involving a broad spectrum of cellular pathways underlying disease progression. Recent investigations indicate that the dysregulation of the sensitive-cysteine proteome may be a concurrent pathogenic mechanism contributing to the pathophysiology of major neurodegenerative diseases, opening new therapeutic opportunities. Considering the incidence and prevalence of these disorders and their already significant burden in Western societies, they will become a real pandemic in the following decades. Therefore, we propose large-scale investigations, in selected groups of people over 40 years of age with decreased blood glutathione levels, comorbidities, and/or mild cognitive impairment, to evaluate supplementation of the diet with low doses of N-acetyl-cysteine, a promising and well-tolerated therapeutic agent suitable for long-term use.

Multivariate Optimization of the Refolding Process of an Incorrectly Folded Fc-Fusion Protein in a Cell Culture Broth

BACKGROUND

Protein misfolding is a common problem in large-scale production of recombinant proteins, which can significantly reduce the yield of the process.

OBJECTIVE

In this work, we aimed at treating a cell culture broth containing high levels (>45%) of incorrectly folded Fc-fusion proteins by a simple redox buffer system in order to increase the proportion of the protein with correct conformation.

METHODS

Multi-variable process optimization was firstly conducted at a small scale (25 mL), employing an experimental design methodology. After identifying the key variables using a resolution IV Fractional Factorial Design (FFD), the process was then optimized by the Central Composite Design (CCD).

RESULTS

The optimal conditions for the refolding reaction were 340 mM Tris-base, 6.0 mM L-cysteine, 0.5 mM L-cystine, a buffer pH of 9.0, a reaction temperature of 8.5ºC and a reaction time of 24 h. Based on the treatment conditions obtained at a small scale, the process was further scaled up to 4500- L. The misfolded content was always less than 20%. The reaction can proceed well in the absence of chemical additives, such as chaotropic agents, aggregation suppressors, stabilizers and chelators.

CONCLUSION

The refolding process increases the fraction of active protein in the original broth reducing the burden on downstream purification steps markedly.

Excretion of human beta-endorphin into culture medium by using outer membrane protein F as a fusion partner in recombinant Escherichia coli

Escherichia coli BL21 strains were found to excrete a large amount of outer membrane protein F (OmpF) into culture medium during high-cell-density cultivation. From this interesting phenomenon, a novel and efficient OmpF fusion system was developed for the excretion of recombinant proteins by E. coli. The ompF gene of E. coli BL21(DE3) was first knocked out by using the red operon of bacteriophage lambda to construct E. coli MBEL-BL101. For the excretion of human beta-endorphin as a model protein, the beta-endorphin gene was fused to the C terminus of the E. coli ompF gene by using a linker containing the Factor Xa recognition site. To develop a fed-batch culture condition that allows efficient production of OmpF-beta-endorphin fusion protein, three different feeding strategies, an exponential feeding strategy and two pH-stat strategies with defined and complex nutrient feeding solutions, were examined. Among these, the pH-stat feeding strategy with the complex nutrient feeding solution resulted in the highest productivity (0.33 g of protein per liter per h). Under this condition, up to 5.6 g of OmpF-beta-endorphin fusion protein per liter was excreted into culture medium. The fusion protein was purified by anion-exchange chromatography and cleaved by Factor Xa to yield beta-endorphin, which was finally purified by reverse-phase chromatography. From 2.7 liters of culture supernatant, 545.4 mg of beta-endorphin was obtained.