LT subunit (A + B)

Heat-labile enterotoxin (LT) is a heat-labile enterotoxin secreted by Enterotoxigenic E.coli (ETEC), which is an AB5-type heterohexameric protein composed of two subunits, LTA and LTB. It is one of the most potent mucosal immunogens and mucosal immune adjuvants that are currently found, and the LTB subunit is one of the most potent mucosal immunogen and adjuvant. Animal immunization has experimentally confirmed that LT holotoxin molecules are significantly more immunogenic than LTB subunit pentamers.
The LTB subunit binds to GM1 gangliosides that are widely distributed on the surface of mammalian cells, resulting in internalization and absorption of the LTA subunit. The LTA subunit is mainly related to its enterotoxin activity and has ADP-ribosyltransferase activity, which is a toxic site of the toxin. The LTB subunit has a non-toxic, strong immunogenicity and can be used as a transport carrier for protective antigens, and the antigen gene can be expressed by fusion with the LTB gene by genetic engineering.