Protein A Protein A is a 42 kDa protein1,2 that is covalently linked to the peptidoglycan layer of the cell wall via the pentaglycin bridge.3 It contains little or no carbohydrate and has a protein structure that is readily accessible for cross-linking procedures. The protein can be obtained at very high purity by lysostaphin digestion of the bacteria followed by gel filtration and affinity chromatography on IgG-agarose. Protein A is stable over an extremely wide pH range (0.99 - 11.8) and is quite resistant to heat and other denaturing agents.4 Binding of protein A to the Fc region of the antibody is not affected by EDTA, non-ionic detergents, or temperatures up to 37°C. Furthermore, Protein A is easily renatured, even after treatment with 4 M urea, 6 M guanidine HCl, or 4 M thiocyanate. Read more...
PANSORBIN® The efficacy of protein A-bearing S. aureus cells as a solid-phase IgG-binding reagent was first demonstrated by Jonsson and Kronvall12 who described a procedure for the quantitation of a-fetoprotein in human serum. This was followed by two publications by Kessler13,14 extolling the advantages of the fixed-cell preparation as an adjunct to immunoprecipitation procedures. In a model system, he described the parameters of antibody and antigen-antibody interactions with protein A-bearing S. aureus cells. He compared this to the conventional method of second antibody precipitation and demonstrated bound protein A's superiority with respect to rapidity and recovery.13 Kessler14 also described the isolation of a number of cell-membrane antigens using rabbit, sheep, goat, or mouse antisera and protein A-bearing S. aureus cells. Read more...
Protein G Protein G (Cat. Nos. 539302 and 539303) is a 23 kDa (34 - 36 kDa apparent M.W. by SDS-PAGE) cell-surface protein from group G Streptococcus species. Like protein A, protein G binds to the Fc portion of immunoglobulins from various species. Protein G or its bacterial form can be used for nearly all applications to which proteins are applied. Immobilized protein G can be used to detect, quantify, and purify IgG antibodies and antigen/antibody complexes. Protein G binds antibodies over a wide range of pH from 4.0 - 8.0, and bound antibodies can be eluted at about pH 2.5 - 3.0. Labeled purified protein G is also versatile and efficient detector of IgG in a variety of immunoassays.20Read more...
Affinities of Protein A and Protein G for Antibodies from Various Species
Species
Affinity for Protein A*
Affinity for Protein G
Human
+ + + +
+ + + +
Rabbit
+ + + +
+ + +
Guinea Pig
+ + + +
+ +
Pig
+ + +
+ + +
Horse
+ +
+ + + +
Cow
+ +
+ + + +
Mouse
+ +
+ + +
Hamster
+
+ +
Sheep
±
+ +
Rat
±
+ +
Goat
–
+ + +
Chicken
–
±
Dog
+ + +
+
Cat
+
–
Monkey
+ + + +
+ + +
Binding of Protein A and Protein G to Various Subclasses of Immunoglobulins 14,26,55,72-76
