Ganglioside GD1a Is an Essential Coreceptor for Toll-like Receptor 2 Signaling in Response to the B subunit of Type IIb Enterotoxin

Department of Microbiology and Immunology, University of Louisville, Louisville, Kentucky, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 04/2007; 282(10):7532-42. DOI: 10.1074/jbc.M611722200
Source: PubMed


Innate recognition and signaling by Toll-like receptors (TLRs) is facilitated by functionally associated coreceptors, although
the cooperativity mechanisms involved are poorly understood. As a model we investigated TLR2 interactions with the GD1a ganglioside
binding subunit of type IIb Escherichia coli enterotoxin (LT-IIb-B5). Both LT-IIb-B5 and a GD1a binding-defective mutant (LT-IIb-B5(T13I)) could modestly bind to TLR2, but only the wild-type molecule displayed a dramatic increase in TLR2 binding activity
in the presence of GD1a (although not in the presence of irrelevant gangliosides). Moreover, fluorescence resonance energy
transfer experiments indicated that LT-IIb-B5 induces lipid raft recruitment of TLR2 and TLR1 and their clustering with GD1a, in contrast to the GD1a binding-defective
mutant, which moreover fails to activate TLR2 signaling. LT-IIb-B5-induced cell activation was critically dependent upon the Toll/IL-1 receptor domain-containing adaptor protein, which was
induced to colocalize with TLR2 and GD1a, as shown by confocal imaging. Therefore, GD1a provides TLR2 coreceptor function
by enabling the ligand to recruit, bind, and activate TLR2. These findings establish a model of TLR2 coreceptor function and,
moreover, suggest novel mechanisms of adjuvanticity by non-toxic derivatives of type II enterotoxins dependent upon GD1a/TLR2
cooperative activity.

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