PCYT1B and vibrio infectious disease: Diarrheal diseases that are initiated in this way account for around two million deaths annually.[1] For example, cholera is caused by an AB5 protein toxin that has a single toxic A-subunit associated with five nontoxic B-subunits (CTB), which constitute a pentameric receptor for the GM1 glycolipid found on the surface of intestinal epithelial cells.[2] Multivalent binding between CTB and up to five copies of its GM1 ligand facilitates the entry of the toxin into the cell by endocytosis.