ng the molecular syringe from the bacterium and studying it under the electron microscope. "We, however, actually studied the injectisome in situ, in other words, on the bacterial surface, right where it normally occurs," explains Prof. Henning Stahlberg, University of Basel. To this end, the researchers cooled the bacteria to minus 193 degrees Celsius and used cryo-electron microscopy to take pictures of the syringe from various angles. They then computed a spatial structure from a set of two-dimensional images -- a highly effective method for examining large molecular complexes. The syringe, which consists of some 30 different proteins, definitely falls into that category.
When comparing over 2000 single syringes from over 300 bacteria, the researchers made a surprising discovery: "There is a range of different lengths of each injection apparatus' base -- in some cases, it's on the order of ten nanometers, or ten millionth of a millimeter. It can be stretched or compressed -- just like a spring," explains Dr. Stefan Schmelz of the HZI, one of the study's first authors. As much as we consider such dimensions to be miniscule -- to a bacterium, which itself is but a hundred times that size, they are substantial. "Bacteria are exposed to considerable forces, be it during contact with other cells or upon changes in environmental salinity," explains Prof. Dirk Heinz, the HZI's scientific director and former head of the HZI Department of Molecular Structural Biology. "If the injectisomes were rigidly constructed, bacteria would most likely be unable to resist these forces. Their cell walls would simply rupture."
Insights into the structure of Yersinia's attack tool offer clues as to ways in which the molecular syringe may be therapeutically inhibited. Without this apparatus, the bacteria are practically harmless. "Also other pathogenic bacteria make use of this principle during infection, for example Salmonella that cause food poisoning," confirmPage: 1 2 3 Related biology news :1
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