B subunit of Escherichia coli heat-labile enterotoxin (EtxB (or LTB))

The B subunit of Escherichia coli heat-labile enterotoxin (EtxB/LTB) is one of five identical polypeptides forming the pentameric binding portion of the AB5-type heat-labile enterotoxin produced mainly by enterotoxigenic E. coli (ETEC). The B subunit pentamer binds to the GM1 ganglioside receptor on mammalian cell membranes, facilitating entry of the enzymatic A subunit (responsible for ADP-ribosylation and elevated cAMP). While the A subunit confers toxicity, the B subunit alone is non-toxic but can modulate immune functions, notably by inducing regulatory T cells and serving as a vaccine adjuvant. The B subunit is structurally homologous to the B subunit of cholera toxin, forming a donut-shaped pentamer stabilized by extensive inter-subunit interactions. Recombinant EtxB/LTB is studied for its potent adjuvant properties and ability to deliver antigens to immune cells without the toxic effects seen with holotoxin.

Other names

EtxBLTBLT-BHeat-labile enterotoxin subunit BEnterotoxin B subunitB chain of LT

Binds host cell GM1 ganglioside, mediating internalization of the entire enterotoxin complex. Delivers the enzymatic A subunit into cells, triggering elevation of cAMP and chloride secretion in ETEC infection. Alone (without A subunit), induces T regulatory cells, modulates immune responses, serves as an adjuvant