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Cargo-transport by coupled molecular motors

Background: In biological systems, energetic processes are typically “quantized” by the hydrolysis of adenosine triphosphate (ATP) molecules enabling elementary reactions and conformation changes of proteins. In this way, molecular motors step discontinuously along cytoskeletal filaments in order to transport cargos such as vesicles or to translate filaments for cytoskeletal reorganization. Most motors operate in groups and thereby enable a more efficient cargo transport.

Problem: The observable fingerprints of the step-wise movement of the cargo remains hidden, since it is very difficult to show coordinated stepping of motors, revealing a synchronization between the proteins, by tracking either the motors or the cargo.

Approach: We perform experiments and simulations/theory to investigate such problems:

a)   We use 3D optical trapping and tracking of 1µm sized beads attached to the tip of a retracting filopodium. Temporal and spatial analysis of the bead’s position fluctuations reveal discontinuous movement from molecular motors operating inside the cell.

b)   We investigate the degree of synchronization for elastically coupled motors stepping in a coordinated manner during cargo transport. The synchronization parameter q helps to identify coupled processes, which are often covered in a diffusion governed environment and which are difficult to extract from measured fluctuation time series.









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