What is the Difference Between Protein A and Protein G?

Protein A and Protein G are bacterial cell wall proteins that have primary binding sites for mammalian, including human, IgG antibodies. They are both used to purify IgG subtype antibodies or in biosensor development. However, there are some differences between them:

• Origin: Protein A is originally found on the cell wall of the bacteria Staphylococcus aureus, while Protein G is isolated from Streptococcal bacteria strains.
• Affinity: Protein A has greater affinity for rabbit, pig, dog, and cat IgG, whereas Protein G has greater affinity for mouse and human IgG. These affinities overlap, but they are general guidelines.
• Binding Strength: The interaction between protein A or G and the affinity matrix can alter the binding strength. For example, rat IgG1 binds to Protein G Sepharose but not to Protein A Sepharose.
• Recombinant Forms: Scientists have engineered recombinant protein A and G that lack albumin binding sites and cell wall binding regions to prevent nonspecific binding during bioassays.
• Protein A/G: This is a recombinant fusion protein that includes the IgG-binding domains of both Protein A and Protein G, making it ideal for binding a broad range of IgG subclasses from various species.

When purchasing protein A or protein G commercially, the specific binding characteristics of the protein will be available in the accompanying information.

Comparative Table: Protein A vs Protein G

Protein A and Protein G are bacterial cell wall proteins that have primary binding sites for mammalian IgG antibodies. They are often used commercially to purify IgG subtype antibodies or in biosensor development. Although they have slightly different affinities for IgG subclasses across different species, they are generally interchangeable for most applications. Here is a comparison of their differences:

The table below shows the binding affinities of Protein A and Protein G to different IgG subclasses across various species:

• = Strong binding affinity, ** = Moderate binding affinity, *** = Weak binding affinity, **** = Very weak binding affinity, x = No binding affinity.