ROBERT LONGUEHAYE, NIBSC / SCIENCE PHOTO LIBRARY ROBERT LONGUEHAYE, NIBSC / SCIENCE PHOTO LIBRARY
Diphtheria toxin. Molecular graphic of the diphtheria toxin in closed (left) and open form. This lethal toxin is secreted by the bacteria Corynebacterium diphtheriae, which causes a life- threatening form of throat infection. The molecule consists of three protein domains: receptor- binding (red), catalytic (green) and transmembrane (blue). The amino acid tryptophan is shown in yellow. The toxin exists in a closed form (left) at neutral pH and an open form at low pH, when pairs of molecules join to form dimers. It blocks protein synthesis in cells but can be neutralized with an antitoxin obtained from immunized horses.
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