Crystal structure of a new heat-labile enterotoxin, LT-IIb

Akker, F. van den; Sarfaty, Steve; Twiddy, E M; Connell, John W.; Holmes, Randall K.; Hól, Wim G. J.

doi:10.1016/s0969-2126(96)00073-1

Cited by 70 publications

(94 citation statements)

References 65 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…LT-IIb-B 5 and other B pentamers of heat-labile enterotoxins can participate in both hydrophilic and hydrophobic interactions (42,43). The so-called "lower end" of the B pentamer pore of LT-IIb interacts through hydrophilic interactions with the extracytoplasmic oligosaccharide moiety of GD1a, which is anchored to the cell membrane via an intramembrane ceramide lipid.…”

Section: Discussionmentioning

confidence: 99%

“…The so-called "lower end" of the B pentamer pore of LT-IIb interacts through hydrophilic interactions with the extracytoplasmic oligosaccharide moiety of GD1a, which is anchored to the cell membrane via an intramembrane ceramide lipid. The "upper end" of the B pentamer pore contains a large hydrophobic surface (549 Å 2 ) that engages in hydrophobic interactions with the A2 subcomponent of the A subunit; however, this hydrophobic surface area is solvent-accessible in the absence of the A subunit (42,43). Because of the absence of an A subunit, LT-IIb-B 5 might, therefore, be free to interact with TLR2 or other receptors that depend on hydrophobic interactions for ligand binding (44 -46).…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

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

Liang

Wang

Tapping

et al. 2007

Journal of Biological Chemistry

View full text Add to dashboard Cite

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.Recent developments in the field of innate immunity support the concept that cellular activation by microbial molecules involves interactions with multiple cooperating host receptors within membrane lipid rafts, whereas single receptor-based interactions may often represent an oversimplified model (1-3). This concept is exemplified by the ability of patternrecognition receptors such as Toll-like receptor 4 (TLR4) 2 or TLR2 to functionally associate with accessory molecules or coreceptors for induction of intracellular signaling. TLR4 alone is not sufficient for inducing a vigorous innate response to lipopolysaccharide (LPS) and requires MD-2 and CD14, although additional components of the LPS recognition complex may play a role in modifying TLR4-mediated signaling (4, 5). TLR2 responds to microbial lipoproteins in association with TLR1 or TLR6 as signaling partners and with CD14 or CD36 as important coreceptors for robust activation of TLR2/1 or TLR2/6 complexes (1, 6). The formation of TLR complexes with coreceptors may serve to generate a combinatorial repertoire for discriminating among the abundant and diverse microbial molecules and thereby to appropriately tailor the host response. However, the mechanisms involved in TLR cooperativity with accessory receptors are currently poorly understood.We have recently shown that the B subunit of type IIb heatlabile enterotoxin of Escherichia coli (designated LT-IIb-B 5 ) activates TLR2 signaling, although the underlying mechanism was not addressed (7). Type IIb and related enterotoxins (types I and IIa) display an AB 5 oligomeric structure in which a toxic A subunit is noncovalently linked to a pe...

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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

Liang

Wang

Tapping

et al. 2007

Journal of Biological Chemistry

View full text Add to dashboard Cite

show abstract

“…Both the structures and functions of the type II HLT are related to the structures and functions of type I HLT (27,54). Type I and type II HLT are oligomeric proteins composed of an A polypeptide which is noncovalently coupled to a pentameric array of B polypeptides.…”

mentioning

confidence: 99%

Mutants of Type II Heat-Labile Enterotoxin LT-IIa with Altered Ganglioside-Binding Activities and Diminished Toxicity Are Potent Mucosal Adjuvants

et al. 2007

View full text Add to dashboard Cite

The structure and function LT-IIa, a type II heat-labile enterotoxin of Escherichia coli, are closely related to the structures and functions of cholera toxin and LT-I, the type I heat-labile enterotoxins of Vibrio cholerae and enterotoxigenic Escherichia coli, respectively. While LT-IIa is a potent systemic and mucosal adjuvant, recent studies demonstrated that mutant LT-IIa(T34I), which exhibits no detectable binding activity as determined by an enzyme-linked immunosorbent assay, with gangliosides GD1b, GD1a, and GM1 is a very poor adjuvant.

show abstract

“…6A); this result is unlikely to reflect residual catalytic activity because LT-IIb-B 5 behaved similarly to LT-IIb(S59K/ E110K). In this regard, we have shown that low-level cAMP induction by LT-IIb-B 5 probably involves TLR2-dependent production of PGE 2 (Fig. 6B, inset) because inhibition of PGE 2 synthesis by indomethacin also inhibited cAMP induction by LT-IIb-B 5 (Fig.…”

Section: Construction Of Mutagenically Detoxified Mutants Of Lt-iibmentioning

confidence: 82%

“…1). The actual catalytic moiety is the A1 subcomponent, which is formed by proteolytic cleavage and reduction of an intrachain disulfide bond in the A polypeptide, while the A2 subcomponent at the C-terminal end of the A polypeptide is inserted noncovalently into the central pore of the ring-shaped B pentamer (2,3). The B pentamer in itself is nontoxic but binds with high affinity to gangliosides, a heterogeneous family of glycolipids found on most cells (4), and delivers the A subunit into the cells (1).…”

mentioning

confidence: 99%

The A Subunit of Type IIb Enterotoxin (LT-IIb) Suppresses the Proinflammatory Potential of the B Subunit and Its Ability to Recruit and Interact with TLR2

Liang

Wang²,

Triantafilou

et al. 2007

The Journal of Immunology

View full text Add to dashboard Cite

The type IIb heat-labile enterotoxin of Escherichia coli (LT-IIb) and its nontoxic pentameric B subunit (LT-IIb-B5) display different immunomodulatory activities, the mechanisms of which are poorly understood. We investigated mechanisms whereby the absence of the catalytically active A subunit from LT-IIb-B5 renders this molecule immunostimulatory through TLR2. LT-IIb-B5, but not LT-IIb, induced TLR2-mediated NF-κB activation and TNF-α production. These LT-IIb-B5 activities were antagonized by LT-IIb; however, inhibitors of adenylate cyclase or protein kinase A reversed this antagonism. The LT-IIb antagonistic effect is thus likely dependent upon the catalytic activity of its A subunit, which causes elevation of intracellular cAMP and activates cAMP-dependent protein kinase A. Consistent with this, a membrane-permeable cAMP analog and a cAMP-elevating agonist, but not catalytically defective point mutants of LT-IIb, mimicked the antagonistic action of wild-type LT-IIb. The mutants moreover displayed increased proinflammatory activity compared with wild-type LT-IIb. Additional mechanisms for the divergent effects on TLR2 activation by LT-IIb and LT-IIb-B5 were suggested by findings that the latter was significantly stronger in inducing lipid raft recruitment of TLR2 and interacting with this receptor. The selective use of TLR2 by LT-IIb-B5 was confirmed in an assay for IL-10, which is inducible by both LT-IIb and LT-IIb-B5 at comparable levels; TLR2-deficient macrophages failed to induce IL-10 in response to LT-IIb-B5 but not in response to LT-IIb. These differential immunomodulatory effects by LT-IIb and LT-IIb-B5 have important implications for adjuvant development and, furthermore, suggest that enterotoxic E. coli may suppress TLR-mediated innate immunity through the action of the enterotoxin A subunit.

show abstract

Crystal structure of a new heat-labile enterotoxin, LT-IIb

Abstract: The structure of LT-IIb provides insight into the sequence diversity and structural similarity of the AB5 toxin family. New knowledge has been gained regarding the assembly of AB5 toxins and their active-site architecture.

Cited by 70 publications

References 65 publications

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

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

Mutants of Type II Heat-Labile Enterotoxin LT-IIa with Altered Ganglioside-Binding Activities and Diminished Toxicity Are Potent Mucosal Adjuvants

The A Subunit of Type IIb Enterotoxin (LT-IIb) Suppresses the Proinflammatory Potential of the B Subunit and Its Ability to Recruit and Interact with TLR2

Contact Info

Product

Resources

About