Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 111, Issue 9, Pages 3436-3441Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1317741111
Keywords
molecular motor; nano-machine; Na+-driven flagella; hybrid-fuel motor; stator dynamics
Categories
Funding
- Japan Society for the Promotion of Science (JSPS) [25840054]
- Uehara Memorial Foundation
- Murata Overseas Scholarship Foundation
- Ministry of Education, Culture, Sports, Science, and Technology [24115518]
- Biotechnology and Biological Sciences Research Council
- Engineering and Physical Sciences Research Council
- BBSRC [BB/H01991X/1, BB/E00458X/1] Funding Source: UKRI
- Grants-in-Aid for Scientific Research [25840054, 24115518] Funding Source: KAKEN
- Biotechnology and Biological Sciences Research Council [BB/E00458X/1, BB/H01991X/1] Funding Source: researchfish
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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.
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