Downstream protein separation by surfactant precipitation: a review

Insulin fibrillation under physicochemical parameters of bioprocessing and intervention by peptides and surface-active agents

Even after the centenary celebration of insulin discovery, there prevail challenges concerning insulin aggregation, not only after repeated administration but also during industrial production, storage, transport, and delivery, significantly impacting protein quality, efficacy, and effectiveness. The aggregation reduces insulin bioavailability, increasing the risk of heightened immunogenicity, posing a threat to patient health, and creating a dent in the golden success story of insulin therapy. Insulin experiences various physicochemical and mechanical stresses due to modulations in pH, temperature, ionic strength, agitation, shear, and surface chemistry, during the upstream and downstream bioprocessing, resulting in insulin unfolding and subsequent fibrillation. This has fueled research in the pharmaceutical industry and academia to unveil the mechanistic insights of insulin aggregation in an attempt to devise rational strategies to regulate this unwanted phenomenon. The present review briefly describes the impacts of environmental factors of bioprocessing on the stability of insulin and correlates with various intermolecular interactions, particularly hydrophobic and electrostatic forces. The aggregation-prone regions of insulin are identified and interrelated with biophysical changes during stress conditions. The quest for novel additives, surface-active agents, and bioderived peptides in decelerating insulin aggregation, which results in overall structural stability, is described. We hope this review will help tackle the real-world challenges of insulin aggregation encountered during bioprocessing, ensuring safer, stable, and globally accessible insulin for efficient management of diabetes.

Nisin Purification from a Cell-Free Supernatant by Electrodialysis in a Circular Economy Framework

Nisin, an antimicrobial peptide produced by Lactococcus lactis strains, is a promising natural preservative for the food industry and an alternative to antibiotics for the pharmaceutical industry against Gram-positive bacteria. Nisin purification is commonly performed using salting out and chromatographic techniques, which are characterized by their low yields, the use of solvents and the production of large volumes of effluents. In the present work, the purification of nisin from a cell-free supernatant (CFS), after the production of nisin by fermentation on a whey permeate medium, was studied using ammonium sulfate precipitation and electrodialysis (ED) as a promising eco-friendly process for nisin purification. Results showed an increase in nisin precipitation using a 40% ammonium sulfate saturation (ASS) level with a purification fold of 73.8 compared with 34.5 and no purification fold for a 60% and 20% ASS level, respectively. The results regarding nisin purification using ED showed an increase in nisin purification and concentration fold, respectively, of 21.8 and 156 when comparing the final product to the initial CFS. Nisin-specific activity increased from 75.9 ± 4.4 to 1652.7 ± 236.8 AU/mg of protein. These results demonstrated the effectiveness of ED coupled with salting out for nisin purification compared with common techniques. Furthermore, the process was noteworthy for its relevance in a circular economy scheme, as it does not require any solvents and avoids generating polluting effluents. It can be employed for the purification of nisin and the recovery of salts from salting out, facilitating their reuse in a circular economy.

Adaptation of the binding domain of Lactobacillus acidophilus S-layer protein as a molecular tag for affinity chromatography development

Introduction

The S-layer proteins are a class of self-assembling proteins that form bi-dimensional lattices named S-Layer on the cell surface of bacteria and archaea. The protein SlpA, which is the major constituent of the Lactobacillus acidophilus S-layer, contains in its C-terminus region (SlpA^{284 - 444}), a protein domain (named here as SLAP_TAG) responsible for the association of SlpA to the bacterial surface. SLAP_TAG was adapted for the development of a novel affinity chromatography method: the SLAP_TAG-based affinity chromatography (SAC).

Methods

Proteins with different molecular weights or biochemical functions were fused in-frame to the SLAP_TAG and efficiently purified by a Bacillus subtilis-derived affinity matrix (named Bio-Matrix or BM). Different binding and elution conditions were evaluated to establish an optimized protocol.

Results

The binding equilibrium between SLAP_TAG and BM was reached after a few minutes of incubation at 4°C, with an apparent dissociation constant (K_D) of 4.3μM. A reporter protein (H6-GFP-SLAP_TAG) was used to compare SAC protein purification efficiency against commercial immobilized metal affinity chromatography. No differences in protein purification performance were observed between the two methods. The stability and reusability of the BM were evaluated, and it was found that the matrix remained stable for more than a year. BM could be reused up to five times without a significant loss in performance. Additionally, the recovery of bound SLAP-tagged proteins was explored using proteolysis with a SLAP-tagged version of the HRV-3c protease (SLAP_ASE). This released the untagged GFP while the cut SLAP_TAG and the SLAP_ASE were retained in the BM. As an alternative, iron nanoparticles were linked to the BM, resulting in BM_mag. The BM_mag was successfully adapted for a magnetic SAC, a technique with potential applications in high-throughput protein production and purification.

Discussion

The SAC protocol can be adapted as a universal tool for the purification of recombinant proteins. Furthermore, the SAC protocol utilizes simple and low-cost reagents, making it suitable for in-house protein purification systems in laboratories worldwide. This enables the production of pure recombinant proteins for research, diagnosis, and the food industry.

Staphylococcus aureus-targeting peptide/surfactant assemblies for antibacterial therapy

To address the challenge from microbial resistance, this work developed a surfactant with 18-carbon single hydrocarbon chain and multi-amine head groups (C18N3). After assembling with Staphylococcus aureus-targeting peptide (CARG), the obtained C18N3/CARG assemblies exhibited excellent antimicrobial activities against Staphylococcus aureus and methicillin-resistant Staphylococcus aureus in vitro and in vivo, in which the targeting peptide CARG bonded specifically to Staphylococcus aureus and C18N3 killed bacteria with a mechanism of membrane disruption. Importantly, C18N3 could also work as a β-lactamase inhibitor to overcome the bacterial resistance to β-lactam antibiotics through noncompetitive inhibition. The combination of β-lactam antibiotic and C18N3/CARG assemblies more effectively suppressed methicillin-resistant Staphylococcus aureus in vitro and in vivo relative to equivalent dose of free antibiotic or C18N3. Thus, the antibacterial platform of antibiotic-carrying surfactant assemblies bearing bacteria-targeted peptides, in which C18N3 performed dual function, antibacterial agent and β-lactamase inhibitor, may help fight against the difficult-to-treat infections.

Separation of Albumin from Bovine Serum Applying Ionic-Liquid-Based Aqueous Biphasic Systems

In this work, the extraction and separation of bovine serum albumin (BSA) from its original matrix, i.e., bovine serum, was performed using a novel ionic-liquid-based aqueous biphasic system (IL-based ABS). To this end, imidazolium-, phosphonium-, and ammonium-based ILs, combined with the anions’ acetate, arginate and derived from Good Buffers, were synthesized, characterized, and applied in the development of ABS with K2HPO4/KH2PO4 buffer aqueous solutions at pH 7. Initial studies with commercial BSA revealed a preferential migration of the protein to the IL-rich phase, with extraction efficiencies of 100% obtained in a single-step. BSA recovery yields ranging between 64.0% and 84.9% were achieved, with the system comprising the IL tetrabutylammonium acetate leading to the maximum recovery yield. With this IL, BSA was directly extracted and separated from bovine serum using the respective ABS. Different serum dilutions were further investigated to improve the separation performance. Under the best identified conditions, BSA can be extracted from bovine serum with a recovery yield of 85.6% and a purity of 61.2%. Moreover, it is shown that the BSA secondary structure is maintained in the extraction process, i.e., after being extracted to the IL-rich phase. Overall, the new ABS herein proposed may be used as an alternative platform for the purification of BSA from serum samples and can be applied to other added-value proteins.

An electrochemical sensor for voltammetric detection of ciprofloxacin using a glassy carbon electrode modified with activated carbon, gold nanoparticles and supramolecular solvent

A highly sensitive and novel electrochemical sensor for ciprofloxacin (CIP) has been developed using gold nanoparticles deposited with waste coffee ground activated carbon on glassy carbon electrode (AuNPs/AC/GCE) and combined with supramolecular solvent (SUPRAS). The fabricated AuNPs/AC/GCE displayed good electrocatalytic activity for AuNPs. The addition of SUPRAS, prepared from cationic surfactants namely didodecyldimethylammonium bromide (DDAB) and dodecyltrimethylammonium bromide (DTAB), increased the electrochemical response of AuNPs. The detection of CIP was based on the decrease of the cathodic current of AuNPs. The electrochemical behavior of the modified electrode was investigated using cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. Under optimum conditions, the calibration plot of CIP exhibited a linear response in the range 0.5-25 nM with a detection limit of 0.20 nM. The fabricated electrochemical sensor was successfully applied to determine CIP in milk samples with achieved recoveries of 78.6-110.2% and relative standard deviations of <8.4%. The developed method was also applied to the analysis of pharmaceutical formulation and the results were compared with high-performance liquid chromatography.Graphical abstract.

Biocompatible Solvents and Ionic Liquid-Based Surfactants as Sustainable Components to Formulate Environmentally Friendly Organized Systems

In this review, we deal with the formation and application of biocompatible water-in-oil microemulsions commonly known as reverse micelles (RMs). These RMs are extremely important to facilitate the dissolution of hydrophilic and hydrophobic compounds for biocompatibility in applications in drug delivery, food science, and nanomedicine. The combination of two wisely chosen types of compounds such as biocompatible non-polar solvents and ionic liquids (ILs) with amphiphilic character (surface-active ionic liquids, SAILs) can be used to generate organized systems that perfectly align with the Green Chemistry concepts. Thus, we describe the current state of SAILs (protic and aprotic) to prepare RMs using non-polar but safe solvents such as esters derived from fatty acids, among others. Moreover, the use of the biocompatible solvents as the external phase in RMs and microemulsions/nanoemulsions with the other commonly used biocompatible surfactants is detailed showing the diversity of preparations and important applications. As shown by multiple examples, the properties of the RMs can be modified by changes in the type of surfactant and/or external solvents but a key fact to note is that all these modifications generate novel systems with dissimilar properties. These interesting properties cannot be anticipated or extrapolated, and deep analysis is always required. Finally, the works presented provide valuable information about the use of biocompatible RMs, making them a green and promising alternative toward efficient and sustainable chemistry.

Determination of Critical Micelle Concentration from the Diffusion-Driven Dilution of Micellar Aqueous Mixtures

Micellization is a phenomenon of central importance in surfactant solutions. Here, we demonstrate that the diffusion-based spreading of the free boundary between a micellar aqueous solution and pure water yields a one-dimensional spatial profile of surfactant concentration that can be used to identify the critical micelle concentration, here denoted as C*. This can be achieved because dilution of micelles into water leads to their dissociation at a well-defined position along the concentration profile and an abrupt increase in the diffusion coefficient. Rayleigh interferometry was successfully employed to determine C* values for three well-known surfactants in water at 25 °C: Triton X-100 (TX-100), sodium dodecyl sulfate (SDS), and poly(oxyethylene)(4)Lauryl Ether (Brij-30). The dependence of C* on salt concentration was also characterized for TX-100 in the presence of Na₂SO₄, NaCl, and NaSCN. Accurate values of C* can be directly identified by visual inspection of the corresponding concentration-gradient profiles. To apply the method of least squares to experimental concentration profiles, a mathematical expression was derived from Fick's law and the pseudophase separation model of micellization with the inclusion of appropriate modifications. While Rayleigh interferometry was employed in our experiments, this approach can be extended to any experimental technique that yields one-dimensional profiles of surfactant concentration. Moreover, diffusion-driven surfactant disaggregation is precise, noninvasive, requires single-sample preparation, and applies to both nonionic and ionic surfactants. Thus, this work provides the foundation of diffusion-driven dilution methods, thereby representing a valuable addition to existing techniques for the determination of C*.

Protein Purification Technologies

Protein Biotechnology is an exciting and fast- growing area of research, with numerous industrial applications. The growing demand for developing efficient and rapid protein purification methods is driving research and growth in this area. Advances and progress in the techniques and methods of protein purification have been such that one can reasonably expect that any protein of a given order of stability may be purified to currently acceptable standards of homogeneity. However, protein manufacturing cost remains extremely high, with downstream processing constituting a substantial proportion of the overall cost. Understanding of the methods and optimization of the experimental conditions have become critical to the manufacturing industry in order to minimize production costs while satisfying the quality as well as all regulatory requirements. New purification processes exploiting specific, effective and robust methods and chromatographic materials are expected to guide the future of the protein purification market.

Protein crystallisation facilitated by silica particles to compensate for the adverse impact from protein impurities

Nanonucleants for protein crystallisation in the presence of impurities.

Influence factors on the critical micelle concentration determination using pyrene as a probe and a simple method of preparing samples

The critical micelle concentration (CMC) is an important parameter of widely used surfactants and needs to be measured in the application and development of surfactants. Fluorometric method is a widely used method determining CMC values owing to the advantages of highly sensitivity, fast response and wide application range. There are two common methods (I and II) of preparing samples for CMC fluorometric determination. In the process of developing CMC probes with aggregation-induced emission (AIE) characteristics, we found that methods I and II were not suitable for CMC probes with AIE charateristics and developed a new sample preparation method (III), which is not only suitable for CMC probes with AIE characteristic but also decreases operation procedures and errors owing to omitting the addition of micro amount of dyes into each sample. To ascertain if method III is also suitable for other CMC probes without AIE characteristics, the CMC values of surfactants were determined by fluorometric method using widely used pyrene without AIE charateristic as probe and methods I-III to prepare samples. The obtained experimental results proved that method III not only was suitable for preparation of samples for CMC determination of surfactants using pyrene as probe but also led to the least average deviation (methods I-III led to ±0.13, ±0.34 and ±0.05 mM deviation for the CMC determination of sodium dodecyl sulfate (SDS), respectively). The CMC determination using pyrene as probe is based on its change in the ratio (I FIII/I FI) of its emission peaks I and III with surfactant concentration. Unexpectedly, it was found that the I FIII/I FI value of pyrene in surfactant solutions is sensitive to the measurement conditions changing exciting light energy, such as slit widths and sample-measured number. In addition, it was found that surfactant SDS or cetrimonium bromide from different suppliers not only has significantly different CMC values but also leads to very different I FIII/I FI values of pyrene in a certain concentration of surfactant, which can be used as a simple method to distinguish the same surfactant with different CMC values.

Determining the Critical Micelle Concentration of Surfactants by a Simple and Fast Titration Method

Critical micelle concentration (CMC) is a crucial parameter of widely used surfactants, and many methods have been developed for CMC determination. However, the current methods for CMC determination, such as conductive, surface tension, and fluorometric methods, are tedious and time- and sample-consuming because a series of samples with different concentrations of surfactants need to be prepared and measured. Although an economical, simple, and fast titration method for CMC determination (only one sample and several minutes are needed) was reported using changes in the color/fluorescence of ionic organic dyes, it has not been used in practical CMC determination owing to the disadvantages of these dyes: very narrow application range (only suitable for cationic or anionic surfactants) and difficult to identify titration end point, especially using different concentrations (10-300 μM) for the same kind surfactants. Here a C6-unsubstituted tetrahydropyrimidine (THP-T1) was found to possess unique and excellent characteristics in titrated surfactant solutions: above CMC, preferring to dissolve in micelles and showing no emission, and not until near/at CMC, being released from micelles and instantly forming aggregates with strong fluorescence. The fluorescence-turn-on change at CMC (titration end point) is so sensitive that it can be clearly observed without comparison of blank and control of dye concentration, and the concentration (c'_THP) of THP-T1 in titrated solution at CMC is only about 1 μM for zwitterionic surfactants and 2.5 μM for other kinds of surfactants. The CMC values determined by the THP-T1-based titration method are almost the same as those determined by the fluorometric method using THP-T1 as probe. THP-T1 overcomes the disadvantages of reported dyes for CMC titration and realizes the economical, simple and fast CMC titration of different kinds of surfactants for the first time.

Application of experimental designs and response surface methods in screening and optimization of reverse micellar extraction

Reverse micellar extraction (RME) has emerged as a versatile and efficient tool for downstream processing (DSP) of various biomolecules, including structural proteins and enzymes, due to the substantial advantages over conventional DSP methods. However, the RME system is a complex dependency of several parameters that influences the overall selectivity and performance of the RME system, hence this justifies the need for optimization to obtain higher possible extraction results. For the last two decades, many experimental design strategies for screening and optimization of RME have been described in literature. The objective of this article is to review the use of different experimental designs and response surface methodologies that are currently used to screen and optimize the RME system for various types of biomolecules. Overall, this review provides the rationale for the selection of appropriate screening or optimization techniques for the parameters associated with both forward and backward extraction during the RME of biomolecules.

Protein crystal occurrence domains in selective protein crystallisation for bio-separation

Bio-separation is a key bottleneck in the manufacture of biopharmaceuticals.

Comparison of Different Nisin Separation and Concentration Methods: Industrial and Cost-Effective Perspectives

Separation and concentration of biotechnological products are the most important steps of purification stage in downstream processing. In the present study, three nisin separation and concentration methods including salting out by ammonium sulfate, solvent extraction (at 20 °C, 4 °C, and - 10 °C) and direct chromatography of culture medium were compared with each other. According to our results, nisin precipitation by ammonium sulfate at 40% saturation was the most efficient method (yield = 90.04%, purification fold = 168.80). Low yield and fold purification values were obtained by solvent extraction with chloroform (yield = 24.23%, fold purification = 37.43 at - 10 °C) and direct cation exchange chromatography of culture medium (yield = 20.00%, fold purification = 1.80). Also, performing purification steps in low pH values and acidic conditions (pH = 3.0) is essential for efficient nisin purification.