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

✍ Scribed by Sarah Spiegel

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 591 KB
• Volume: 42
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.240420305

✦ Synopsis

The use of the B subunit of cholera toxin, a protein that binds specifically to ganglioside GM 1, has provided a new paradigm for studying physiological functions of ganglioside GMl . 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 independent 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 (SDS-PAGE) 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.