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What are the differences between protein A and protein G?
Posted January 22, 2024

Answer

Protein A:

  • Is a surface protein originally found in the cell wall of Staphylococcus aureus
  • Has a molecular size of 42kDa
  • Is expressed by Staphylococcus aureus
  • Does not have binding sites for serum albumin
  • Can be used to purify human antibodies such as IgA, IgM, and IgE because it has a higher ability to bind to human antibodies other than IgG antibody
  • Cannot be used for purification of the human IgG3 subclass as it cannot bind to the human IgG3 subclass immunoglobulin.

Protein G:

  • Is a surface immunoglobulin binding protein specifically expressed by group C and D streptococcal bacteria
  • Has a molecular size of approximately 65kDa
  • Is expressed by group C and D streptococcal bacteria
  • Has binding sites for serum albumin
  • Can be used to purify the human IgG3 subclass as it is binding to the human IgG3 subclass immunoglobulin
  • Can bind to all subtypes of human IgG antibodies but not to other human antibodies such as IgA, IgE, and IgM 
  • Cannot be used to purify these human antibodies IgA, IgE and IgM