Differential effect of polyol and sugar osmolytes on the refolding of homologous alpha amylases: A comparative study

Phycocyanin from microalgae: A comprehensive review covering microalgal culture, phycocyanin sources and stability

As food safety continues to gain prominence, phycocyanin (PC) is increasingly favored by consumers as a natural blue pigment, which is extracted from microalgae and serves the dual function of promoting health and providing coloration. Spirulina-derived PC demonstrates exceptional stability within temperature ranges below 45 °C and under pH conditions between 5.5 and 6.0. However, its application is limited in scenarios involving high-temperature processing due to its sensitivity to heat and light. This comprehensive review provides insights into the efficient production of PC from microalgae, covers the metabolic engineering of microalgae to increase PC yields and discusses various strategies for enhancing its stability in food applications. In addition to the most widely used Spirulina, some red algae and Thermosynechococcus can serve as good source of PC. The genetic and metabolic manipulation of microalgae strains has shown promise in increasing PC yield and improving its quality. Delivery systems including nanoparticles, hydrogels, emulsions, and microcapsules offer a promising solution to protect and extend the shelf life of PC in food products, ensuring its vibrant color and health-promoting properties are preserved. This review highlights the importance of metabolic engineering, multi-omics applications, and innovative delivery systems in unlocking the full potential of this natural blue pigment in the realm of food applications, provides a complete overview of the entire process from production to commercialization of PC, including the extraction and purification.

Rate of dilution and redox ratio influence the refolding efficiency of recombinant fungal dehydrogenases

Dehydrogenases from fungi are attracting attention as industrial biocatalysts due to their high activity and chiral selectivity. However, these enzymes form insoluble aggregates when overexpressed in E. coli, limiting their industrial application. In the present study, we report the systematic development of a refolding process for selected, industrially relevant fungal dehydrogenases, viz., formate dehydrogenase from Candida boidinii (CbFDH) and formate and alcohol dehydrogenases from Geotrichum candium (GcFDH and GcADH, respectively). We first employed a screen to evaluate the effects of different variables on refolding including the buffer system, additives, and rate of dilution. The extent of refolding was determined by enzyme assays, circular dichroism, and tryptophan fluorescence. Our results showed that glycerol and reducing environment are essential for refolding of these dehydrogenases. Further, slow dilution of solubilized protein over 16 h dramatically improved the recovery of refolded enzymes compared to rapid dilution. The importance of slow dilution was further confirmed in a 10-fold scaled-up refolding trial. Overall, we demonstrate a robust method for refolding of fungal dehydrogenases, thus improving their availability for various biocatalytic applications.

Spectroscopic analysis of recombinant human growth hormone in the presence of sucrose and trehalose

Recombinant human growth hormone (rhGH) is a therapeutic protein, associated with various human diseases, such as growth hormone deficiency. One of the interesting issues in the formulation of therapeutic proteins is excipients like disaccharides. In the current study, we try to compare the effect of sucrose and trehalose on the structure of rhGH in the liquid state at 25°C and 55°C. We use spectroscopic techniques including intrinsic and extrinsic fluorescence, Fourier-transform infrared (FTIR), circular dichroism (CD), dynamic light scattering (DLS), and time-resolved fluorescence. FTIR shows a slight change in the secondary structure of rhGH in presence of the sugars as sucrose is more effective than trehalose. Fluorescence investigations also confirm the enhancements of folding of rhGH and fluorescein isothiocyanate (FITC)-rhGH in presence of sucrose (1.5-fold more than trehalose). Also, we studied sucrose's effect on the rete of aggregation of rhGH using spectroscopy of Congo red, and fluorescence imaging of thioflavin T (ThT)-treated samples. It can be suggested that sucrose facilitates the amyloid formation of rhGH during 20 days of incubation at 37°C. This study will help to understand the growth hormone structural behavior in the liquid state in the presence of sucrose and trehalose in vitro.

Kinetic control in amyloid polymorphism: Different agitation and solution conditions promote distinct amyloid polymorphs of alpha-synuclein

Aggregation of neuronal protein α-synuclein is implicated in synucleinopathies, including Parkinson's disease. Despite abundant in vitro studies, the mechanism of α-synuclein assembly process remains ambiguous. In this work, α-synuclein aggregation was induced by its constant mixing in two separate modes, either by agitation in a 96-well microplate reader (MP) or in microcentrifuge tubes using a shaker incubator (SI). Aggregation in both modes occurred through a sigmoidal growth pattern with a well-defined lag, growth, and saturation phase. The end-stage MP- and SI-derived aggregates displayed distinct differences in morphological, biochemical, and spectral signatures as discerned through AFM, proteinase-K digestion, FTIR, Raman, and CD spectroscopy. The MP-derived aggregates showed irregular morphology with a significant random coil conformation, contrary to SI-derived aggregates, which showed typical β-sheet fibrillar structures. The end-stage MP aggregates convert to β-rich SI-like aggregates upon 1) seeding with SI-derived aggregates and 2) agitating in SI. We conclude that end-stage MP aggregates were in a kinetically trapped conformation, whose kinetic barrier was bypassed upon either seeding by SI-derived fibrils or shaking in SI. We further show that MP-derived aggregates that form in the presence of sorbitol, an osmolyte, displayed a β-rich signature, indicating that the preferential exclusion effect of osmolytes helped overcome the kinetic barrier. Our findings help in unravelling the kinetic origin of different α-synuclein aggregated polymorphs (strains) that encode diverse variants of synucleinopathies. We demonstrate that kinetic control shapes the polymorphic landscape of α-synuclein aggregates, both through de novo generation of polymorphs, and by their interconversion.

Effects of Chemical Additives in Refolding Buffer on Recombinant Human BMP-2 Dimerization and the Bioactivity on SaOS-2 Osteoblasts

Bone morphogenetic protein-2 (BMP-2) is a promising osteogenic agent in tissue engineering. BMP-2 is usually expressed in Escherichia coli owing to the high yield and low cost, but the protein is expressed as inclusion bodies. Thus, the bottleneck for BMP-2 production in E. coli is the refolding process. Here, we explored the effects of the refolding buffer composition on BMP-2 refolding. The BMP-2 inclusion body was solubilized in urea and subjected to refolding by the dilution method. Various additives were investigated to improve the BMP-2 refolding yield. Nonreducing SDS-PAGE showed that BMP-2 dimers, the presumably biologically active form, were detected at approximately 25 kDa. The highest yield of the BMP-2 dimers was observed in the refolding buffer that contained ionic detergents (sarkosyl and cetylpyridinium chloride) followed by zwitterionic and nonionic detergents (NDSB-195, NP-40, and Tween 80). In addition, sugars (glucose, sorbitol, and sucrose) in combination with anionic detergents (sodium dodecyl sulfate and sarkosyl) reduced BMP-2 oligomers and increased the BMP-2 dimer yield. Subsequently, the refolded BMP-2s were tested for their bioactivity using the alkaline phosphatase assay in osteogenic cells (SaOS-2), as well as the luciferase reporter assay and the calcium assays. The refolded BMP-2 showed the activities in the calcium deposition assay and the luciferase reporter assay but not in the alkaline phosphatase activity assay or the intracellular calcium assay even though the dimers were clearly detected. Therefore, the detection of the disulfide-linked dimeric BMP-2 in nonreducing SDS-PAGE is an inadequate proxy for the bioactivity of BMP-2.

Refolding in the modern biopharmaceutical industry

Inclusion bodies (IBs) often emerge upon overexpression of recombinant proteins in E. coli. From IBs, refolding is necessary to generate the native protein that can be further purified to obtain pure and active biologicals. This work focusses on refolding as a significant process step during biopharmaceutical manufacturing with an industrial perspective. A theoretical and historical background on protein refolding gives the reader a starting point for further insights into industrial process development. Quality requirements on IBs as starting material for refolding are discussed and further economic and ecological aspects are considered with regards to buffer systems and refolding conditions. A process development roadmap shows the development of a refolding process starting from first exploratory screening rounds to scale-up and implementation in manufacturing plant. Different aspects, with a direct influence on yield, such as the selection of chemicals including pH, ionic strength, additives, etc., and other often neglected aspects, important during scale-up, such as mixing, and gas-fluid interaction, are highlighted with the use of a quality by design (QbD) approach. The benefits of simulation sciences (process simulation and computer fluid dynamics) and process analytical technology (PAT) for seamless process development are emphasized. The work concludes with an outlook on future applications of refolding and highlights open research inquiries.

Polyol and sugar osmolytes stabilize the molten globule state of α-lactalbumin and inhibit amyloid fibril formation

Protein misfolding and aggregation are associated with several human diseases such as Alzheimer's, Parkinson's, prion related disorders, type-II diabetes, etc. Different strategies using molecular chaperones, synthetic and naturally occurring small molecules, osmolytes, etc. have been used to prevent protein aggregation and amyloid fibril formation. In this study, we have used bovine α-lactalbumin at pH 1.6, 37 °C, and shaking conditions to promote amyloid fibril formation. Polyol and sugar osmolytes like glycerol, sorbitol, and trehalose have been used to inhibit the fibrillation of a number of proteins. In the present work, amyloid fibril formation of α-lactalbumin has been shown by ThT assay and AFM, while changes in the secondary structure during fibrillation has been followed by circular dichroism spectroscopy. Our results show that glycerol, sorbitol, and trehalose affect amyloid fibril formation of α-lactalbumin in a concentration-dependent manner. There is a delay in the lag phase of amyloid fibril formation in sorbitol and trehalose and complete inhibition in 6 M glycerol. Our results indicate that delay in the lag phase and inhibition of amyloid fibril formation are due to the stabilization of molten globule state by these osmolytes. At pH 1.6, the molten globule as well as the amyloid fibrils bind to ANS. However, when pH was shifted from 1.6 to 7, only the oligomeric and the fibrillar species bind to ANS due to refolding of molten globule state. The outcome of this study might be useful in designing small molecules which may stabilize the intermediate states, thus preventing amyloid fibril formation.

Role of molecular and chemical chaperon in assisting refolding of BMP2 in E. coli

Bone morphogenetic protein 2 (BMP2) when expressed in bacteria forms inclusion bodies (IBs) due to its complex disulfide-rich structure. Chaperons are already well known for their role in assisting protein folding. In our studies, we have used two E. coli strains, BL21(DE3) and SHuffle® T7 cells for overexpressing BMP2 in soluble fraction. We observed that SHuffle® T7 cells successfully expressed soluble functionally active BMP2 in presence of molecular and chemical chaperones at low temperature. The combination of chemical and molecular chaperons further increases the yield of protein. The best-suited chaperon system for overexpression of BMP2 is GroES-GroEL at low temperature. The soluble functionally active BMP2 is confirmed by its binding to its receptor ALK3 through Native PAGE and ELISA assay using BMP2 specific antibody. It is possible to obtain BMP2 expression in soluble active form by using molecular and chemical chaperons which work synergistically in bacterial cells to fold disulphide-rich proteins at low temperature in easy and time saving steps (18 ̊C).

Structural and functional adaptation in extremophilic microbial α-amylases

Maintaining stable native conformation of a protein under a given ecological condition is the prerequisite for survival of organisms. Extremophilic bacteria and archaea have evolved to adapt under extreme conditions of temperature, pH, salt, and pressure. Molecular adaptations of proteins under these conditions are essential for their survival. These organisms have the capability to maintain stable, native conformations of proteins under extreme conditions. The enzymes produced by the extremophiles are also known as extremozyme, which are used in several industries. Stability and functionality of extremozymes under varying temperature, pH, and solvent conditions are the most desirable requirement of industry. α-Amylase is one of the most important enzymes used in food, pharmaceutical, textile, and detergent industries. This enzyme is produced by diverse microorganisms including various extremophiles. Therefore, understanding its stability is important from fundamental as well as an applied point of view. Each class of extremophiles has a distinctive set of dominant non-covalent interactions which are important for their stability. Static information obtained by comparative analysis of amino acid sequence and atomic resolution structure provides information on the prevalence of particular amino acids or a group of non-covalent interactions. Protein folding studies give the information about thermodynamic and kinetic stability in order to understand dynamic aspect of molecular adaptations. In this review, we have summarized information on amino acid sequence, structure, stability, and adaptability of α-amylases from different classes of extremophiles.