Protein G is an immunoglobulin-binding protein expressed in group C and G Streptococcal bacteria. It is a 65-kDa (G148 protein G) and a 58 kDa (C40 protein G) cell surface protein that has found application in purifying antibodies through its binding to the Fc region .
Protein G binds to most mammalian IgGs through the Fc region, but some binding also occurs through the Fab region.
Native protein G also binds albumin, however, because serum albumin is a major contaminant of antibody sources, the albumin binding site has been removed from recombinant forms of Protein G .
Protein G / Agarose from InvivoGen uses the recombinant form of protein G lacking the albumin-binding region.
- Sjobring U. et al., 1991. Streptococcal Protein G. Gene structure and protein binding properties. J Biol Chem. 140:1194-1197.
- Goward CR. et al., 1990. Expression and purification of truncated recombinant streptococccal Protein G. Biochem J. 267:171-177.