Mono-sized microspheres modified with poly(ethylenimine) facilitate the refolding of like-charged lysozyme

Fabrication of a Heptapeptide-Modified Poly(glycidyl Methac-Rylate) Nanosphere for Oriented Antibody Immobilization and Immunoassay

Oriented antibody immobilization has been widely employed in immunoassays and immunodiagnoses due to its efficacy in identifying target antigens. Herein, a heptapeptide ligand, HWRGWVC (HC7), was coupled to poly(glycidyl methacrylate) (PGMA) nanospheres (PGMA-HC7). The antibody immobilization behavior and antigen recognition performance were investigated and compared with those on PGMA nanospheres by nonspecific adsorption and covalent coupling via carbodiimide chemistry. The antibodies tested included bovine, rabbit, and human immunoglobulin G (IgG), while the antigens included horseradish peroxidase (HRP) and β-2-Microglobulin (β2-MG). The nanospheres were characterized using zeta potential and particle size analyzers, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and reversed-phase chromatography, proving each synthesis step was succeeded. Isothermal titration calorimetry assay demonstrated the strong affinity interaction between IgG and PGMA-HC7. Notably, PGMA-HC7 achieved rapid and extremely high IgG adsorption capacity (~3 mg/mg) within 5 min via a specific recognition via HC7 without nonspecific interactions. Moreover, the activities of immobilized anti-HRP and anti-β2-MG antibodies obtained via affinity binding were 1.5-fold and 2-fold higher than those of their covalent coupling counterparts. Further, the oriented-immobilized anti-β2-MG antibody on PGMA-HC7 exhibited excellent performance in antigen recognition with a linear detection range of 0-5.3 μg/mL, proving its great potential in immunoassay applications.

Charge modifications of graphene oxide enhance the inhibitory effect on insulin amyloid fibrillation based on electrostatic interactions

Graphene oxide (GO) is a biocompatible nanomaterial that has an inhibitory effect on insulin amyloid fibrillation. In order to enhance the inhibitory effect of GO and explore the rules of electrostatic interactions on the inhibitory effect, carboxyl group, PEI and PEG were coupled to the GO nanoplatelet surface to prepare inhibitors of different surface electrical properties. The effects of surface electrical properties of inhibitors on insulin fibrillation were investigated. The results showed that GO, carboxyl group modified GO (GO-COOH), PEI modified GO (GO-PEI), and PEG modified GO (GO-PEG) inhibited insulin fibrillation in a dose-dependent manner. Compared with GO, positive charge-modified GO-PEI and negative charge-modified GO-COOH enhanced the inhibitory effect, while uncharged polymer-modified GO-PEG weakened the inhibitory effect. The inhibitory effect of the inhibitors increased with the increase of surface charge density. The difference in inhibitory effect between GO-PEI and GO-COOH was due to the different electrostatic interactions between inhibitors and insulin, and the different inhibition mechanisms. In addition, inhibitors mainly interact with insulin during the nucleation phase to hinder insulin fibrillation. The charge modifications of graphene oxide enhanced the inhibitory effect on insulin fibrillation based on electrostatic interactions, which will provide new thoughts for the development of anti-amyloid fibrillation drugs.

Characterization of a heptapeptide-modified microsphere for oriented antibody immobilization

Oriented immobilization of antibodies is important for the effective recognition of target antigens. In this paper, a heptapeptide ligand, HWRGWVC (HC7), was modified onto non-porous mono-sized poly (glyceryl methacrylate) (pGMA) microspheres (named pGMA-HC7) to explore the antibody immobilization behaviors. Characterization of the microspheres by particle size analyzer, scanning electron microscopy, Fourier transform infrared spectroscopy, and reversed-phase chromatography proved the success of each fabrication step. The capacity and activity of antibody immobilization through HC7 were studied using immunoglobulin G (IgG) as a model antibody and horseradish peroxidase (HRP) as a model antigen. Additionally, IgG immobilizations on pGMA microspheres by nonspecific adsorption and covalent coupling through carbodiimide chemistry were conducted for comparison. pGMA-HC7 exhibited an IgG adsorption capacity of 3-4 mg/g in 10 min by the specific binding of HC7 without nonspecific interactions. Notably, the ligand HC7 showed a by two orders of magnitude stronger affinity for IgG than its original hexapeptide ligand HWRGWV. Moreover, the capacity and activity of the immobilized anti-HRP antibody on pGMA-HC7 were 1.6-fold and 3-fold higher than those of the covalent coupling, respectively. The results proved the superior role of HWRGWVC in the affinity binding of antibody and the potential of pGMA-HC7-25 in immunoassay and immunodiagnostic applications.

Enzyme-support interactions and inactivation conditions determine Thermomyces lanuginosus lipase inactivation pathways: Functional and florescence studies

Lipase from Thermomyces lanuginosus (TLL) has been covalently immobilized on heterofunctional octyl-vinyl agarose. That way, the covalently immobilized enzymes will have identical orientation. Then, it has blocked using hexyl amine (HEX), ethylenediamine (EDA), Gly and Asp. The initial activity/stability of the different biocatalysts was very different, being the most stable the biocatalyst blocked with Gly. These biocatalysts had been utilized to analyze if the enzyme activity could decrease differently along thermal inactivation courses depending on the utilized substrate (that is, if the enzyme specificity was altered during its inactivation using 4 different substrates to determine the activity), and if this can be altered by the nature of the blocking agent and the inactivation conditions (we use pH 5, 7 and 9). Results show great changes in the enzyme specificity during inactivation (e.g., activity versus triacetin was much more quickly lost than versus the other substrates), and how this was modulated by the immobilization protocol and inactivation conditions. The difference in the changes induced by immobilization and inactivation were confirmed by fluorescence studies. That is, the functional and structural analysis of partially inactivated immobilized enzyme showed that their inactivation pathway is strongly depended on the support features and inactivation conditions.

Charged Surface Regulates the Molecular Interactions of Electrostatically Repulsive Peptides by Inducing Oriented Alignment

Regulation of molecular orientation of charged dipeptides and involved interactions by electrostatic repulsion from like-charged surfaces were studied using all-atom molecular dynamics simulations. It was found that a charged surface can induce oriented alignment of like-charged peptides, and the oriented alignment leads to enhanced electrostatic repulsion between the peptide molecules. The findings are consistent with previous experimental results about the inhibition of charged protein aggregation using like-charged ion-exchange resin. Furthermore, the simulations provided molecular insights into this process, and demonstrated the distinct regulation effect of like-charged surfaces on the molecular interactions between peptides that possess an electric dipole structure. Both the charged surface and the electric dipole structure of peptides were confirmed to be crucial for the regulation. The research is expected to facilitate the rational design of surfaces or devices to regulate the behavior of amphoteric molecules such as proteins for both in vivo and in vitro applications, which would contribute to the regulation of protein-protein interactions and its application in life science and biotechnology.

Reversible Immobilization of Lipases on Heterofunctional Octyl-Amino Agarose Beads Prevents Enzyme Desorption

Two different heterofunctional octyl-amino supports have been prepared using ethylenediamine and hexylendiamine (OCEDA and OCHDA) and utilized to immobilize five lipases (lipases A (CALA) and B (CALB) from Candida antarctica, lipases from Thermomyces lanuginosus (TLL), from Rhizomucor miehei (RML) and from Candida rugosa (CRL) and the phospholipase Lecitase Ultra (LU). Using pH 5 and 50 mM sodium acetate, the immobilizations proceeded via interfacial activation on the octyl layer, after some ionic bridges were established. These supports did not release enzyme when incubated at Triton X-100 concentrations that released all enzyme molecules from the octyl support. The octyl support produced significant enzyme hyperactivation, except for CALB. However, the activities of the immobilized enzymes were usually slightly higher using the new supports than the octyl ones. Thermal and solvent stabilities of LU and TLL were significantly improved compared to the OC counterparts, while in the other enzymes the stability decreased in most cases (depending on the pH value). As a general rule, OCEDA had lower negative effects on the stability of the immobilized enzymes than OCHDA and while in solvent inactivation the enzyme molecules remained attached to the support using the new supports and were released using monofunctional octyl supports, in thermal inactivations this only occurred in certain cases.