What are the similarities between protein A and protein G?

Protein A and protein G are both microbial proteins. Both are also recombinant proteins. Both types of proteins have primary binding sites for mammalian immunoglobulin G (IgG) antibodies, including human IgG. Both, protein A and protein G can bind to the Fc region of immunoglobulins and both are used for immunoglobulins purification.