Temporally resolved molecular motor dynamics: A case of ncd-microtubule interactions

Molecular motors and the associated microfilaments play an important role in cell division, intracellular transport and signaling, and are fundamental to such neuronal functions as bidirectional protein transport to and from the periphery of neural cells. A number of neurological diseases have been linked to the abnormal function of molecular motors acting upon microtubules and an improved understanding of the role of various molecular motors has been recently cited as one of the new frontiers of neuroscience. Details of molecular motor-microtubule interactions on a single molecular level can be revealed during optical trapping experiments. Until recently, low signal-to-noise ration of optical trap data required analysis by ensemble averaging, which obscures interaction details and masks infrequent sub-categories of interaction events. In this note, we summarize a recently developed method that allowed us to reveal the details of single molecular motor-microtubule interactions as a function of time based on a time series of the measurements without averaging. This method was applied to Kinesin-14 Ncd in three-bead optical trap geometry and it was found that, contrary to previous results obtained by ensemble averaging, the ncd power strokes are bidirectional, with the majority of strokes directed towards the minus end of the microtubule. The developed capability to analyze the molecular motor dynamics without averaging and in real time opens the possibility to study the mechanism of the intracellular transport, cytoskeletal organization, and therapeutic effects on a single molecular level.