Although globotetraosylceramide (Gb
4) is only recognized by a single member of the verotoxin family namely, the pig edema disease toxin (VT2e), removal of the acetyl group from the terminal N-acetyl hexosamine of Gb
4 to generate the free amino sugar containing
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Although globotetraosylceramide (Gb
4) is only recognized by a single member of the verotoxin family namely, the pig edema disease toxin (VT2e), removal of the acetyl group from the terminal N-acetyl hexosamine of Gb
4 to generate the free amino sugar containing species (aminoGb
4) results in the generation of a glycolipid preferentially recognized by all members of the verotoxin family (
i.e., VT1, VT2, VT2c, and VT2e). GT3, a site-specific mutant of VT2e, in which Gb
4 recognition is lost but Gb
3 binding is retained, also binds aminoGb
4. We have now compared the binding of VT1, VT2, VT2e, and GT3 to a series of aminoGb
4 derivatives using a TLC overlay technique. DimethylaminoGb
4 is bound by VT1 and VT2 but not VT2e or GT3; formylaminoGb
4 binds all toxins but poorly to VT2 and preferentially VT2e; trifluoroacetylaminoGb
4 binds only VT2e and GT3; isopropylaminoGb
4 binds VT1 and poorly to VT2; benzylaminoGb
4 binds all four toxins. Thus, there is a marked distinction between the permissible amino substitutions for VT1 and VT2e binding. GT3 is a hybrid between these in that, according to the substitution, it behaves similarly either to VT1 or to VT2e. For each species, GT3 does not however, show a hybrid binding between that of VT1 and VT2e. Analysis of the binding as a function of pH shows opposite effects for VT1 and VT2e: decreased pH increases VT1, but decreases VT2e receptor glycolipid binding.
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