title: Ganglioside GD1a is an essential coreceptor for Toll-like receptor 2 signaling in response to the B subunit of type IIb enterotoxin.
abstract: 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-B(5)). Both LT-IIb-B(5) and a GD1a binding-defective mutant (LT-IIb-B(5)(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-B(5) 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-B(5)-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.
authors.affiliation: Center for Oral Health and Systemic Disease and Department of Periodontics, University of Louisville Health Sciences Center, Louisville, Kentucky 40292, USA.
authors.forename: Shuang
authors.initials: S
authors.lastname: Liang
authors.forename: Min
authors.initials: M
authors.lastname: Wang
authors.forename: Richard I
authors.initials: RI
authors.lastname: Tapping
authors.forename: Vitaly
authors.initials: V
authors.lastname: Stepensky
authors.forename: Hesham F
authors.initials: HF
authors.lastname: Nawar
authors.forename: Martha
authors.initials: M
authors.lastname: Triantafilou
authors.forename: Kathy
authors.initials: K
authors.lastname: Triantafilou
authors.forename: Terry D
authors.initials: TD
authors.lastname: Connell
authors.forename: George
authors.initials: G
authors.lastname: Hajishengallis
mesh_terms: D000818:Animals; D001427:Bacterial Toxins / Q000378:metabolism / Q000494:pharmacology*; D016466:CHO Cells; D019556:COS Cells; D002522:Chlorocebus aethiops; D006224:Cricetinae; D003412:Cricetulus; D004768:Enterotoxins / Q000378:metabolism / Q000494:pharmacology*; D029968:Escherichia coli Proteins / Q000378:metabolism / Q000494:pharmacology*; D005732:Gangliosides / Q000502:physiology*; D006801:Humans; D008562:Membrane Glycoproteins / Q000502:physiology; D021962:Membrane Microdomains / Q000502:physiology; D009000:Monocytes / Q000187:drug effects; D017472:Receptors, Interleukin-1 / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D051194:Toll-Like Receptor 1 / Q000502:physiology; D051195:Toll-Like Receptor 2 / Q000502:physiology*
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D005732:Gangliosides; D008562:Membrane Glycoproteins; D017472:Receptors, Interleukin-1; C434984:TIRAP protein, human; C495342:TLR2 protein, human; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; C021298:ganglioside, GD1a; C027538:heat-labile enterotoxin, E coli