Researchers have determined the three-dimensional structureof a protein similar to cholera toxin, a discovery that may leadto better vaccines and drugs for travelers' diarrhea andcholera, as well as for diphtheria and whooping cough, whichare caused by similar bacterial toxins.

Several companies, including Enterovax Ltd. in Australia andPasteur Vaccins in France, are developing cholera vaccinesthat can be administered orally.

Cholera toxin consists of five B subunits attached to one Asubunit. After the B subunits bind to intestine cells, the Asubunit enters the cells, causing them to secrete fluids. Theloss of fluids causes diarrhea that ranges from mild to fatal.

Researchers at the University of Groningen in the Netherlandsreported last week in Nature on a protein called heat-labileenterotoxin, which has the same structure. They found that thefive B subunits form a doughnut. The long A subunit extendsfrom the hole in the doughnut, attached to the B ring by a hook.

In an accompanying article, Simon van Heyningen of theUniversity of Edinburgh agrees with the authors that thestructure is "quite spectacular." But he questions how theinformation will help the millions of people who suffer fromcholera and are too poor to even obtain rehydration therapy."What they need is not vaccines, but clean water and bettersanitation," he wrote. -- CTV

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