A Nanonewton Optical Force Trap and the Slip-State of Kinesin-8 Motor

Molecular machines are fascinating devices that drive self-organization in cells. While the protein components of many biological machines have been identified, the mechanical principles that govern the operation of biological machines are poorly understood. For example, how much force can they generate; and what limits their speed and efficiency? We use a high-resolution optical tweezers apparatus to measure intermolecular forces that are central to biological questions such as how kinesin motor proteins move and diffuse along microtubules. I will introduce our optical tweezers, recent improvements of the latter, and their use in measuring the nanomechanics of individual kinesins. In particular, our development of antireflection-coated, high-refractive-index titania microspheres enabled us to reach more than a nanonewton in optical force and to measure the colored noise of Brownian motion. Also, a novel slip state of kinesin-8, we argue, acts as a molecular safety leash to enhance the processivity of the motor.