PROTEIN G

What is PROTEIN G

**Introduction to Protein G** Protein G is a highly versatile bacterial cell wall protein derived from *Streptococcus* species, widely used in biotechnology and immunology for its exceptional ability to bind immunoglobulins (IgGs) from multiple species. With high affinity for the Fc region of antibodies, Protein G is a preferred tool for antibody purification, immunoprecipitation, and immunoassays such as ELISA and Western blotting. Unlike Protein A, it exhibits broader species reactivity and stronger binding to certain IgG subclasses, making it invaluable in research and therapeutic applications. Recombinant forms of Protein G are engineered to minimize non-specific interactions, ensuring high purity and efficiency. Its reliability and adaptability have solidified Protein G as a cornerstone in antibody-based workflows. (100 words)

Preparation Process: **Preparation of Protein G:** 1. **Expression:** Clone the Protein G gene into an expression vector (e.g., pET or pGEX) and transform into *E. coli* BL21(DE3) cells. 2. **Induction:** Grow cells in LB medium at 37°C to OD600 ~0.6–0.8, then induce with 0.1–1 mM IPTG at 16–25°C for 4–16 hours. 3. **Harvesting:** Pellet cells by centrifugation (4,000–6,000 ×g, 20 min, 4°C) and lyse using sonication or French press in lysis buffer (e.g., PBS with protease inhibitors). 4. **Purification:** Pass lysate through an IgG-agarose column, wash with buffer, and elute with low-pH (e.g., 0.1 M glycine-HCl, pH 2.7) or imidazole (if His-tagged). 5. **Buffer Exchange:** Dialyze or desalt into PBS or storage buffer (e.g., Tris-HCl, pH 8.0). 6. **Analysis:** Verify purity via SDS-PAGE and concentration by Bradford assay. Store at −20°C or −80°C.

Usage Scenarios: Protein G is a bacterial cell wall protein derived from *Streptococcus* species, widely used in biochemistry and immunology for its high affinity to the Fc region of immunoglobulins. It is primarily employed in antibody purification, immunoprecipitation, and immunoassays (e.g., ELISA, Western blotting) to isolate or detect antibodies with minimal nonspecific binding. Unlike Protein A, Protein G binds a broader range of IgG subtypes, including human, mouse, and rat, making it versatile for research and diagnostic applications. It is also used in affinity chromatography columns and conjugated to beads or fluorescent tags for targeted antibody capture. Its stability and specificity enhance experimental accuracy and efficiency.

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