Cholera enterotoxin subunit B (CTXB) is also known as cholera enterotoxin B chain, cholera enterotoxin gamma chain and choleragenoid. Vibrio cholerae O1 exists as two major serotypes, Inaba and Ogawa, which are associated with the O antigen of the lipopolysaccharide and are capable of unequal reciprocal interconversion. The B subunit pentameric ring directs the A subunit to its target by binding to the GM1 gangliosides present on the surface of the intestinal epithelial cells. CTXB can bind five GM1 gangliosides. Also, it has no toxic activity by itself.