Mechanism of antibodies purification by protein A

Protein A, a major cell wall component of Staphylococcus aureus, is one of the first immunoglobulin-binding proteins that is discovered about 80 years ago. However, a great deal of development in both purification methods and application of antibodies in treatment have been done. There are many publications based on the untargeted (size exclusion, ion exchange and hydrophobic interactions) and targeted (affinity) methods by scientists in academic/industry groups. In this review, we have focused on the study of both native and engineered Protein A to understand its mechanism in the purification of antibodies. What domain of Protein A dose interact with antibody? Where are contact regions? What is the non-covalent interaction mechanism of Protein A and antibody? Does alkaline condition, in the washing step, influence on antibody structure and activity? On the other hand, the immobilization of Protein A on various sorbents such as agarose, silica, polysaccharide, polymers, and magnetic nanoparticles have investigated. Also, the application of Protein A as biosensor for detection of the antibody is discussed. We have tried to find interesting and stimulating answers to all these questions.

Model Protein BSA Adsorption and Covalent Coupling onto Methyl Methacrylate Based Latex Particles with Different Surface Properties

The adsorption and covalent coupling of bovine serum albumin (BSA) onto methylmethacrylate (MMA) based monodisperse latex particles with different hydrophylic surfaces were investigated. P(MMA) and P(MMA/HEMA) microbeads in the size range of 1.5–2.0 mm were prepared by a dispersion homopolymerization method in the presence of poly(vinylpyrrolidone) (PVP) and poly(vinyl alcohol) (PVA) as steric stabilizer and by copolymerization of MMA and 2-hydroxethyl methacrylate (HEMA) where PVP was used as steric stabilizers. Surface properties of these particles were characterized in terms of contact angle measurements and FTIR-DRS spectra. Additionally, hydroxyl groups of PMMAPVA and P(MMA/HEMA) particles were activated to provide aldehyde groups on surfaces. Adsorption of the BSA onto these five types of latex particles was examined as a function of initial albumin concentration, pH and ionic strength of the various cations (Na+,Ca+ and Mg− and anions (Cl− and SCN−). The maximum adsorption capacities for all latex particles were obtained in solutions with 0.01μ m ionic strength and 1 mg/mL BSA concentration. When using PMMAPVA, P(MMA/HEMA) and PMMAPVP, the adsorption increased as hydrophobicity increased. Aldehyde activation of the two most hydrophobic particles elevated the coupling (immobilization) significantly in ionic strength of 0.01μ m. The adsorption and/or immobilization were maximum in the presence of monovalent cation, Na+ or anion, Cl−B for all types of latex particles.

Investigation of in vitro interactions between different polymeric surfaces and blood proteins via phagocytosis phenomena

The effect of various polymeric materials on blood components and their in vitro phagocytosis was the object of the present research. Polystyrene- (PS) and polymethylmetacrylate- (PMMA) based microspheres were produced by phase-inversion polymerization and chemically modified to obtain different surface hydrophilicities. The interactions between blood proteins and chemically- and biologically-modified surfaces were investigated and compared to plain microspheres. Adsorption properties of albumin, fibrinogen and total immunoglobulines on microspheres were tested. Hydrophilic surfaces have high ability for human serum albumin (HSA) adsorption, which also leads to less phagocytosis of microspheres in vitro. In the case of activated PMMA(PVA) microspheres, both protein adsorption and phagocytosis were significant. Interaction of blood proteins with microspheres did not cause any change in phagocytosis by leukocytes and monocytes. BSA adsorption on microspheres with different hydrophilicities showed the same blood protein adsorption results and phagocytosis was not detected. On the other hand, the highest level of phagocytosis was found with fibronectin-modified microspheres. The changes occurring in intrinsic and extrinsic coagulation mechanisms were determined by measuring the activated partial tromboplastin time (APTT) and the prothrombin time (PT). PT values of blood samples did not increase by treatment with microspheres, except for PS/HEMA, while chemical modification caused important prolongation in APTT.