When a salmonella bacterium attacks a cell, it uses a nanoscopic needle to inject the cell with proteins to aid the infection. If the needle is too short, the cell won't be infected. If the needle is too long, it breaks. Now, University of Utah biologists report how a disposable molecular ruler or tape measure determines the length of the bacterial needle so it is just right. The findings have potential long-term applications for developing new antibiotics against salmonella and certain other disease-causing bacteria, for designing bacteria that could inject cancer cells with chemotherapy drugs, and for helping people determine how to design machines at the nanoscopic or molecular scale. The study by University of Utah Biology Professor Kelly Hughes and doctoral student Daniel Wee was published online on March 16, 2015 in PNAS. "If you look at important pathogens - the bubonic plague bacterium, salmonella, shigella, and plant pathogens like fire blight - they all use hypodermic-like needles to inject proteins that facilitate disease processes," Dr. Hughes says. "Our work says that there is one mechanism - the molecular ruler - to explain how the lengths are controlled for needles in gram-negative bacteria and for hooks on flagella [the U-joints in propellers bacteria use to move] in all bacteria," he adds. In their study, Wee and Dr. Hughes found that as a bacterial needle or "injectisome" grows, a molecular ruler - really, more like a gooey tape measure - is secreted from within the needle's base. It oozes up through the tube-like needle, and when the bottom end of the ruler reaches the bottom end of the needle, the needle stops growing and begins to inject proteins into the target cell to help the infection process.
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