We have developed an optical trapping method to precisely measure the force generated by motor proteins on single organelles of unknown size in cell extract. This approach, termed VMatch, permits the functional interrogation of native motor complexes. We apply VMatch to measure the force, number and activity of kinesin-1 on motile lipid droplets isolated from the liver of normally fed and food-deprived rats.
Bibliographical noteFunding Information:
We thank A. Rai and R. Jha for discussions and help and K. Verhey (University of Michigan) for kinesin-1 antibody. R.M. acknowledges funding through an International Senior Research Fellowship from the Wellcome Trust, UK (grant WT079214MA).