The maximum number of torque-generation units in the flagellar motor of Escherichia coli is at least 11
Proceedings of the National Academy of Sciences of the USA 103 (2006) 8066-8071
The molecular elasticity of the insect flight muscle proteins projectin and kettin
Proceedings of the National Academy of Sciences of the United States of America 103:12 (2006) 4451-4456
Abstract:
Projectin and kettin are titin-like proteins mainly responsible for the high passive stiffness of insect indirect flight muscles, which is needed to generate oscillatory work during flight. Here we report the mechanical properties of kettin and projectin by single-molecule force spectroscopy. Force-extension and force-clamp curves obtained from Lethocerus projectin and Drosophila recombinant projectin or kettin fragments revealed that fibronectin type III domains in projectin are mechanically weaker (unfolding force, F u ≈ 50-150 pN) than Ig-domains (Fu ≈ 150-250 pN). Among Ig domains in Sls/kettin, the domains near the N terminus are less stable than those near the C terminus. Projectin domains refolded very fast [85% at 15 s-1 (25°C)] and even under high forces (15-30 pN). Temperature affected the unfolding forces with a Q10 of 1.3, whereas the refolding speed had a Q10 of 2-3, probably reflecting the cooperative nature of the folding mechanism. High bending rigidities of projectin and kettin indicated that straightening the proteins requires low forces. Our results suggest that titin-like proteins in indirect flight muscles could function according to a folding-based-spring mechanism. © 2006 by The National Academy of Sciences of the USA.Fluorescence measurement of intracellular sodium concentration in single Escherichia coli cells.
Biophys J 90:1 (2006) 357-365
Abstract:
The energy-transducing cytoplasmic membrane of bacteria contains pumps and antiports maintaining the membrane potential and ion gradients. We have developed a method for rapid, single-cell measurement of the internal sodium concentration ([Na(+)](in)) in Escherichia coli using the sodium ion fluorescence indicator, Sodium Green. The bacterial flagellar motor is a molecular machine that couples the transmembrane flow of ions, either protons (H(+)) or sodium ions (Na(+)), to flagellar rotation. We used an E. coli strain containing a chimeric flagellar motor with H(+)- and Na(+)-driven components that functions as a sodium motor. Changing external sodium concentration ([Na(+)](ex)) in the range 1-85 mM resulted in changes in [Na(+)](in) between 5-14 mM, indicating a partial homeostasis of internal sodium concentration. There were significant intercell variations in the relationship between [Na(+)](in) and [Na(+)](ex), and the internal sodium concentration in cells not expressing chimeric flagellar motors was 2-3 times lower, indicating that the sodium flux through these motors is a significant fraction of the total sodium flux into the cell.Direct observation of steps in rotation of the bacterial flagellar motor
Nature 437 (2005) 916-919
Intracellular sodium concentration of chimera Escherichia coli
FEBS J 272 (2005) 345-346