Overview
Protein A/G is a genetically engineered fusion protein that combines the IgG-binding regions of Staphylococcus aureus Protein A and Streptococcus Protein G. This hybrid molecule exhibits broader antibody-binding capabilities than either protein alone, recognizing a wider range of IgG subclasses from multiple species, including human, mouse, and rabbit. It is commonly produced in E. coli and available as a lyophilized powder or pre-coupled to matrices like agarose beads. Due to its dual-binding domains, Protein A/G is a versatile tool in immunology and biotechnology, offering higher binding capacity and flexibility compared to native Protein A or G. It is widely adopted in research, diagnostic, and therapeutic antibody production workflows.
Physical and Chemical Properties
Protein A/G typically has a molecular weight of 50-60 kDa, though this may vary slightly depending on the expression system and post-translational modifications. The protein is stable in neutral pH buffers (e.g., PBS or Tris-HCl) but may degrade under extreme pH (<3 or >10) or prolonged exposure to reducing agents. Its binding affinity to IgG is pH-dependent, with optimal binding at neutral to slightly alkaline pH (7.4-8.0) and elution possible under acidic conditions (pH 2.5-3.5). The fusion protein retains the Fc-binding specificity of both parent proteins, enabling interactions with IgG heavy chains while avoiding interference from other serum proteins.
Main Applications
In antibody purification, Protein A/G is immobilized on chromatography resins to capture IgG from serum, cell culture supernatants, or hybridoma samples. Its broad species reactivity reduces the need for species-specific purification protocols. For immunoprecipitation (IP), Protein A/G-coupled beads are used to isolate antigen-antibody complexes from lysates, followed by Western blotting or mass spectrometry analysis. In diagnostics, it serves as a detection reagent in ELISA and lateral flow assays due to its consistent binding performance. Therapeutic applications include antibody removal therapies and vaccine development.
Safety and Storage
Protein A/G is generally non-hazardous but should be handled with standard laboratory precautions, including gloves and eye protection. Lyophilized powder is stable at -20°C for years; reconstituted solutions should be aliquoted to avoid repeated freeze-thaw cycles. Contamination risks include endotoxins (critical for in vivo applications) and proteases. Suppliers often provide certificates of analysis (CoA) with endotoxin levels (<1 EU/mg) and purity data. For bead-coupled forms, storage in 20% ethanol at 4°C prevents microbial growth.
B2B Procurement Guide
When sourcing Protein A/G, prioritize suppliers with ISO 13485 or GMP certification for diagnostic/therapeutic applications. Key specifications include binding capacity (≥10 mg IgG/mL resin), endotoxin levels, and absence of carrier proteins (e.g., BSA). Bulk buyers should negotiate volume discounts and request batch-to-batch consistency data. For bead-coupled versions, consider particle size uniformity (e.g., 45-165 µm for flow compatibility). Alternatives like recombinant Protein L (for light-chain binding) may be evaluated for specialized needs.
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