Time-dependent measure of a nanoscale force-pulse driven by the axonemal dynein motors in individual live sperm cells.

Nanoscale mechanical forces generated by motor proteins are crucial to normal cellular and organismal functioning. The ability to measure and exploit such forces is important to developing motile biomimetic nanodevices powered by biological motors for nanomedicine. Axonemal dynein motors positioned inside the sperm flagellum drive microtubule sliding and give rise to rhythmic beating. This force-generating action pushes the sperm cell through viscous media. Here we report new nanoscale information on how the propulsive force is generated by the sperm flagellum and how this force varies over time. Using a modified atomic force microscope, single-cell recordings reveal discrete approximately 50-ms pulses oscillating with amplitude 9.8 +/- 2.6 nN independent of pulse frequency (3.5-19.5 Hz). The average work carried out by each cell is 4.6 x 10(-16) J per pulse, equivalent to the hydrolysis of approximately 5500 molecules of adenosine triphosphate. The mechanochemical coupling at each active dynein head is approximately 2.2 pN per adenosine triphosphate molecule and approximately 3.9 pN per dynein arm. From the clinical editor: In this paper, nanoscale mechanical forces generated by axonemal dynein motors derived from sperm flagellum are examined and reported. These motor proteins are crucial to normal cellular and organismal functioning. The ability to measure and exploit such forces is important to developing motile biomimetic nanodevices powered by biological motors for nanomedicine. 2010 Elsevier Inc. All rights reserved.