Towards real-time 3D Tracking of Structural Transitions in Adenylate Kinase by Thermal Noise Imaging

Proteins in contrast to macroscopic machines are subject to thermal fluctuations in shape which provide both opportunities and challenges. They have to be flexible enough to support turn-over rates up to hundreds per second, yet stable enough to maintain their three-dimensional structure over hours and days. As result of thermal excitation they fluctuate between structural conformations. We measured thermally excited structural fluctuations in the Adenylate Kinase using a site-specifically attached nanoparticle and a laser trap based position sensing scheme. This 'Thermal Noise Imaging' (TNI) can provide real-time tracking of 3D structural transitions. TNI uses scattering of laser light to locate a nanoparticle with {\AA}ngstr{\o}m spatial and microsecond temporal resolution. We present details of the technique and a comparison of thermally excited structure fluctuations with functional transitions.