Application of native polyacrylamide gel electrophoresis for protein analysis: Bovine serum albumin as a model protein

Insights into effects of processing and food matrices on structure and ELISA detection of sarcoplasmic calcium binding protein

The sandwich ELISA (sELISA) targeting sarcoplasmic calcium binding protein (SCP) is significantly influenced by food matrices, yet the mechanisms are unclear. To clarify the comprehensive effects of environments, matrices, and processing, SCP treated with diverse temperatures, pH, and matrices was subjected to ELISA, electrophoresis, multispectroscopic and molecular simulation assays. Recoveries of sELISA and indirect competitive ELISA (icELISA) were inhibited above 80 °C and 100 °C due to the unfolding of SCP. Under acidic conditions, SCP became more compact improving icELISA while reducing sELISA. The tertiary structure, aggregation state of SCP, and ELISA results were primarily impacted by inorganic salts, carbohydrates, and peanut oil via non-covalent interactions. Slighter impacts of processing on icELISA suggested SCP might preserve epitopes maintaining antibody recognition. These findings elucidated the effects of various factors on SCP structure and the mechanisms behind variations in ELISA results, additionally demonstrating the stronger interference resistance of icELISA.

A novel anion replaced gemini surfactant: Investigation on the primary interaction between gemini surfactant and BSA

Gemini surfactants (GS) could serve as the drug carrier agents for the delivery of macromolecules due to the excellent properties and tuneable structures. Little attention has been paid to the impact of counterion change on GS and the interaction between GS and protein. In this work, ibuprofen (Ibu) replaced quaternary ammonium ion GS (GS-Ibu) with the hydrophobic chain length of 8, 10, 12, 14 and 16 carbon atoms were prepared for the first-time using extraction technology. The prepared GS-Ibu has stronger electrostatic interaction compared to traditional gemini surfactants with bromide anions (GS-Br). GS were further incubated with the model macromolecule, bovine serum albumin (BSA), to form BSA/GS complexes. The colloid stability of BSA could be affected by the concentration of GS, the length of hydrophobic chain and the type of anion. GS-Ibu exhibited better ability to prevent BSA from aggregating based the result of PAGE test. The molecular level change of BSA after the introduction of GS was first reflected by UV-Visible absorption spectrum. CD spectrum results further revealed that the primary interaction leading to the change in the secondary structure of BSA is electrostatic interaction. Molecular docking and molecular dynamic simulations confirmed the presence of hydrophobic and electrostatic interaction between BSA and GS. In conclusion, the anion replaced GS could be a promising strategy to stabilize the proteins.

Analysis of proteins by agarose native gel electrophoresis in the presence of solvent additives

Solvent additives, including NaCl, arginine hydrochloride (ArgHCl), glycine and sucrose, are used to enhance protein stability or reduce protein aggregation. Here, we studied the effects of these additives on proteins using agarose native gel electrophoresis. Since these additives are used at relatively high concentration, we first confirmed that they do not interfere with the performance of the native gel electrophoresis. Agarose native gel electrophoresis showed that aggregation of bovine serum albumin (BSA) induced by heating was slightly reduced by NaCl and ArgHCl. On the contrary, glycine and sucrose had marginal effects. ArgHCl and NaCl promoted heat aggregation of monoclonal antibody (mAb), while glycine and sucrose stabilized the native mAb. Arginine methyl ester inhibited heat aggregation of lysozyme and, to a much lesser extent, BSA. These results show that agarose native gel electrophoresis can be used to analyze the effects of solvent additives on proteins subjected to heat stresses. SYPRO Orange that stains only unfolded proteins confirmed unfolded structures of soluble aggregates.

Serum Albumin: A Multifaced Enzyme

Human serum albumin (HSA) is the most abundant protein in plasma, contributing actively to oncotic pressure maintenance and fluid distribution between body compartments. HSA acts as the main carrier of fatty acids, recognizes metal ions, affects pharmacokinetics of many drugs, provides the metabolic modification of some ligands, renders potential toxins harmless, accounts for most of the anti-oxidant capacity of human plasma, and displays esterase, enolase, glucuronidase, and peroxidase (pseudo)-enzymatic activities. HSA-based catalysis is physiologically relevant, affecting the metabolism of endogenous and exogenous compounds including proteins, lipids, cholesterol, reactive oxygen species (ROS), and drugs. Catalytic properties of HSA are modulated by allosteric effectors, competitive inhibitors, chemical modifications, pathological conditions, and aging. HSA displays anti-oxidant properties and is critical for plasma detoxification from toxic agents and for pro-drugs activation. The enzymatic properties of HSA can be also exploited by chemical industries as a scaffold to produce libraries of catalysts with improved proficiency and stereoselectivity for water decontamination from poisonous agents and environmental contaminants, in the so called “green chemistry” field. Here, an overview of the intrinsic and metal dependent (pseudo-)enzymatic properties of HSA is reported to highlight the roles played by this multifaced protein.

Fluorescence-based techniques for the detection of the oligomeric status of proteins: implication in amyloidogenic diseases

Intrinsically disordered proteins (IDPs) have captured attention in the last couple of decades due to their functional roles despite a lack of specific structure. Moreover, these proteins are found to be highly aggregation prone depending on the mutational and environmental changes to which they are subjected. The aggregation of such proteins either in the intracellular context or extracellular matrix is associated with several adverse pathophysiological conditions such as Alzheimer's, Parkinson's, and Huntington's diseases, Spinocerebellar ataxia, and Type-II diabetes. Interestingly, it has been noted that the smaller oligomers formed by IDPs are more toxic to cells than their larger aggregates. This necessitates the development of techniques that can detect the smaller oligomers formed by IDPs for diagnosis of such diseases during their early onset. Fluorescence-based spectroscopic and microscopic techniques are highly effective as compared to other techniques for the evaluation of protein oligomerization, organization, and dynamics. In this review, we discuss several fluorescence-based techniques including fluorescence/Förster resonance energy transfer (FRET), homo-FRET, fluorescence recovery after photobleaching (FRAP), fluorescence correlation spectroscopy (FCS), fluorescence lifetime imaging (FLIM), and photobleaching image correlation spectroscopy (pbICS) that are routinely used to identify protein oligomers in extracellular and intracellular matrices.

Reversible Dimerization of Human Serum Albumin

Pulsed Dipolar Spectroscopy (PDS) methods of Electron Paramagnetic Resonance (EPR) were used to detect and characterize reversible non-covalent dimers of Human Serum Albumin (HSA), the most abundant protein in human plasma. The spin labels, MTSL and OX063, were attached to Cys-34 and these chemical modifications of Cys-34 did affect the dimerization of HSA, indicating that other post-translational modifications can modulate dimer formation. At physiologically relevant concentrations, HSA does form weak, non-covalent dimers with a well-defined structure. Dimer formation is readily reversible into monomers. Dimerization is very relevant to the role of HSA in the transport, binding, and other physiological processes.

Stand-Alone Semi-Solid-State Electrochemical Systems Based on Bicontinuous Microemulsion Gel Films

Bicontinuous microemulsion (BME)-based hydrogel films were integrated with screen-printed electrodes (SPEs) comprising working, counter, and reference electrodes to form stand-alone, semi-solid-state electrochemical systems that do not require an outer electrolyte solution. The gel network of the BME hydrogel only exists in the microaqueous phase and retains the structure of the entire BME gel. Following gelation, a microaqueous phase with sufficient ionic strength ensured effective ionic conductivity, even in thin gel films. This enabled the electrochemical reaction to proceed using a thin gel film as an electrolyte solution. However, an intact micro-oil phase with no gel network enabled efficient extraction from an external oil solution and exhibited rapid electrochemistry that was comparable to that of a BME solution. Cyclic voltammograms of lipophilic redox species in oil using the gel-integrated SPE system demonstrated successfully in the oil itself and in the air with dropped oil onto the system.