Han Zuilhof*,†,‡,§ † Laboratory of Organic Chemistry, Wageningen University, Dreijenplein 8, 6703 HB Wageningen, The Netherlands ‡ School of Pharmaceutical Science and Technology, Tianjin University, Tianjin 300072, China § Department of Chemical and Materials Engineering, King Abdulaziz University, Jeddah, Saudi Arabia
Over the last decades increasing scientific attention has been devoted to systems with fivefold symmetry, with a special interest in, for example, quasi-crystals, Penrose tilings, and related objects.1 This may lead to very beautiful entities, but beauty is in the eyes of the beholder. A still rather imposing beholder is in fact the bacterium Vibrio cholera. This microorganism causes cholera in human beings, and for this it uses a protein with fivefold symmetry, from the class of socalled AB5 proteins.2 After oral intake of polluted water, bacteria that survive the acid in the stomach work their way through the intestinal mucus layer to get close to the intestinal wall. Upon arrival they start to produce the toxic protein, cholera toxin (CT). This toxin (see Figure 1) is composed of five identical host-cell-recognizing subunits (the B proteins) and the toxic A subunit. Binding of the toxin onto the host cell and subsequent uptake into the cell are mediated by a specific pentasaccharide molecule, the so-called GM1 ganglioside. These GM1 molecules reside on the outside of the cell wall as part of the cell’s “sugar coating” (glycocalix), and the five B proteins (CT-B) can bind strongly to them in a hand-in-glove manner (Figure 1c).