Time-Dependent Measure of a Nano-Scale Force-Pulse Driven by the Axonemal Dynein Motors in Individual Live Sperm Cells

Nano-scale 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 nano-scale 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 ~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 ~5,500 ATP molecules. The mechanochemical coupling at each active dynein head is ~2.2 pN/ATP, and ~3.9 pN per dynein arm.