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Protein G (the bacterial antibody binding protein) is often used to pulldown antibodies, for example in chromatin immunoprecipitation (ChIP) experiments.

However, I was unable to find a site describing the history of the said protein, and how the name of Protein G came about, due to the fact that the similarly named (but completely different) G protein came up higher in search results.

What was Protein G named after? For example, Protein A was named after the antibody fraction in which it was found, and G protein was named because it bound GDP and GTP.

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    $\begingroup$ This paper seems to suggest that protein G is so named because it was isolated from group G streptococci. $\endgroup$ – canadianer Oct 12 '15 at 3:12
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    $\begingroup$ @canadianer is correct. Group G comes from Lancefield serum type G and it was a method that used to be used to classify bacterium and Group G Streptococci could be identified using this method. The protein was isolated from G148 S.aureus. Canadianer should post as an answer. +1 $\endgroup$ – AMR Oct 12 '15 at 3:38
  • $\begingroup$ G148 is a Streptococcus strain. I incorrectly used the Genus and Species for Staphylococcus aureus in my prior comment. Protein A was isolated in S.aureus, Protein G in Streptococcus G148. $\endgroup$ – AMR Oct 12 '15 at 19:22
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As @canadianer mentions in his comment, Protein G is more than likely named after the human group G strain of Streptococci, G148.

Protein G, a bacterial cell wall protein with affinity for immunoglobulin G (IgG), has been isolated from a human group G streptococcal strain (G148).

Purification and some properties of streptococcal protein G, a novel IgG-binding reagent. - Björck et.al.

Protein G is a Streptococcus protein that can bind the the Fc portion of the Immunoglobulin G protein. While it is similar to protein A, it was found to have better binding affinities to the different varieties of heavy chain constant regions of IgG molecules.

The G comes from Lancefield grouping. Lancefield grouping was a method that used to be used to classify bacterium. Group G Streptococci could be identified using Lancefield serum type G and that is how they received their classification.

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