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Cautionary note on the use of the B subunit of cholera toxin as a ganglioside GM1 probe: Detection of cholera toxin A subunit in B subunit preparations by a sensitive adenylate cyclase assay
Author(s) -
Spiegel Sarah
Publication year - 1990
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.240420305
Subject(s) - cholera toxin , ganglioside , protein subunit , adenylate kinase , cyclase , biochemistry , gi alpha subunit , g alpha subunit , biology , microbiology and biotechnology , chemistry , enzyme , gene
The Use of the B subunit of cholera toxin, a protein that binds specifically to ganglioside GM1, has provided a new paradigm for studying physiological functions of ganglioside GM1. The B subunit inhibited the growth of rat glioma C6 cells that had been pretreated with ganglioside GM1. In some preparations of the B subunit, the inhibition was endependent of adenylate cyclase activation and was due to the binding of the B subunit to ganglioside GM1 inserted onto the cell surface. However, in other preparations of the B subunit, there was an additional inhibitory effect due to small contaminations with the A subunit, which caused increases in intracellular cyclic adenosine monophosphate (cAMP) levels and concomittant growth inhibition. This vanishingly small contamination with the A subunit could not be detected by conventional protein sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDSPAGE) analysis but could be measured utilizing a sensitive adenylate cyclase activation assay. Thus caution must be used to ensure that any biological effects of the B subunit are not due to contaminating A subunit and are due solely to the binding of the B subunit to ganglioside GM1 exposed on the cell surface. This is especially important in cyclic nucleotide‐sensitive systems.