Hybrid-fuel bacterial flagellar motors in Escherichia coli

作者：Sowa Yoshiyuki^*; Homma Michio; Ishijima Akihiko; Berry Richard M

来源：Proceedings of the National Academy of Sciences of the United States of America, 2014, 111(9): 3436-3441.

DOI：10.1073/pnas.1317741111

• molecular motor
• nano-machine
• Na+-driven flagella
• hybrid-fuel motor
• stator dynamics

The bacterial flagellar motor rotates driven by an electrochemical ion gradient across the cytoplasmic membrane, either H+ or Na+ ions. The motor consists of a rotor similar to 50 nm in diameter surrounded by multiple torque-generating ion-conducting stator units. Stator units exchange spontaneously between the motor and a pool in the cytoplasmic membrane on a timescale of minutes, and their stability in the motor is dependent upon the ion gradient. We report a genetically engineered hybrid-fuel flagellar motor in Escherichia coli that contains both H+- and Na+-driven stator components and runs on both types of ion gradient. We controlled the number of each type of stator unit in the motor by protein expression levels and Na+ concentration ([Na+]), using speed changes of single motors driving 1-mu m polystyrene beads to determine stator unit numbers. De-energized motors changed from locked to freely rotating on a timescale similar to that of spontaneous stator unit exchange. Hybrid motor speed is simply the sum of speeds attributable to individual stator units of each type. With Na+ and H+ stator components expressed at high and medium levels, respectively, Na+ stator units dominate at high [Na+] and are replaced by H+ units when Na+ is removed. Thus, competition between stator units for spaces in a motor and sensitivity of each type to its own ion gradient combine to allow hybrid motors to adapt to the prevailing ion gradient. We speculate that a similar process may occur in species that naturally express both H+ and Na+ stator components sharing a common rotor.

• 出版日期2014-3-4