How much do you know about Protein G?

  • Protein G is a cell wall protein isolated from streptococcus G. Streptococcus protein G is a cell wall protein on the surface of Streptococcus streptococcus, which consists of nearly 600 amino acids. The N-terminal part is albumin binding domain, and the C-terminal part is IgG binding domain and cell wall binding domain. Streptococcal protein G is called a superantigen because of its ability to bind many different antibodies. It is usually called by Protein G, Streptococcal Protein G, Recombinant Streptococcal Protein G.

    Do you know the function of Protein G?

    Recombinant streptococcus protein G can be used to detect, purify and remove antibodies and antibody-antigen complexes, such as the use of recombinant streptococcus protein G is similar to that of recombinant Staphylococcus aureus protein A. Although the industrialization of Staphylococcus aureus protein A is deeper than streptococcal protein G for historical reasons. Generally speaking, protein G is more extensive than protein A in binding to IgG-igG, and the intensity of binding to IgG is stronger.

    Do you know the character of Protein G?

    Unless otherwise required, direct extraction of protein G from streptococcus is extremely rare. Recombinant streptococcal protein G was obtained by removing the albumin binding domain of natural protein and preserving the IgG binding domain. The recombinant DNA technique was used to express and purify the recombinant streptococcus protein. The IgG binding domain of the recombinant protein only maintained about 90% homology with the IgG binding domain, but the binding ability of the antibody was increased by 50% -100%. Protein G node is bound to IgG, IgF of Streptococcus graminearum C, Fab-IgG , IgG Fab', IgG-scFv (ab') 2, trifunctional antibody but not bound to scFv/di-scFv, sdAb/nanobody, BiTE and other types of human antibody IgA, IgD, IgE, IgM.

    Do you know IgG?

    One of the species forms of mammalian antibodies (also known as immunoglobulin, Ig). The antibody associated immunity against pathogen invasion is mainly provided by four types of protein which is the only one that can provide passive immunity to fetus through the placenta.

    IgG acts as an activator of complement, neutralization and a variety of toxins in the immune response. The IgG antibody is the only one that can protect the fetus through the placenta during pregnancy because of its long duration. They also secrete from the mammary gland into colostrum, so that the newborn is protected by antibodies at the first time. IgG is a four-stranded monomer, which accounts for 75% of the total serum Ig. It is the most important antibody component in serum and extracellular fluid, and can be divided into four subclasses of human IgG.

    IgG1, IgG2, IgG3, IgG4 were synthesized three months after birth and close to adult levels between the ages of 3 and 5, depending on the concentration in the serum that mainly produced by plasma cells in spleen and lymph nodes whose half-life of serum is longer, about 20 ~ 23 days. It is the main antibody produced by rehumoral immune response. Its affinity is high and widely distributed in the body who has important immune effect. It is the main force of body anti-infection, so it should be injected once every 2 weeks when immunotherapy with gamma globulin.

    Do you know the function of IgG?

    IgG1, IgG3, IgG4 can go cross the placental barrier and play an important role in neonatal anti-infection immunity, IgG1, IgG2, IgG4 can bind to staphylococcal protein A (SPA) through its Fc segment, which can be used to purify antibodies, or to be used for immunological diagnosis. IgG1, IgG3 can efficiently activate complement and bind to Fc receptor on macrophages and NK cells. Some autoantibodies and antibodies causing type II and III hypersensitivity also belong to IgG.

    Do you know how can we get IgG?

    There are many methods to get IgG. The following method is called crude extraction of globuli. Ammonium sulfate salting-out or sodium sulfate salting-out are mostly used. Ammonium sulfate saltout had to be precipitated many times. The first step was 40% saturation and the second step were 35% saturation, the last was 33% saturation. The γ globulin extracted after three times was basically a IgG component. Sodium sulfate method is more convenient. γ-globulin can be precipitated with 20%. Most of the gamma-globulin after salting out belongs to IgG, but there are 5% other band proteins, such as γ -region heterologous proteins. IgG components also contain other normal IgG, interference. Therefore, the γ -globulin extracted by salting-out method can only be used in general experiments or antibody effects.

    And there is another method to get IgG which is called ion exchange chromatography. And the most frequently used ion-exchange agents are DEAE cellulose or QAE cellulose, among which QAE-Sephadex is the best. Take QAE-SephadexA25 or A50 acid treating. After equilibrium in the phosphate buffer of 0.05mol/LpH7.5~8.6, the water was dried and Ig was added to the serum of 10ml. After 30min at room temperature, the ion exchanger was removed by centrifugation or filtration. The supernatant was treated like this again, And the purified IgG was even free of other proteins. The purification of IgG by this technique is simple without damaging antibody and can be extracted in small quantities or prepared in large quantities.