Surfing along filopodia: A particle transport revealed by molecular-scale fluctuation analyses
05.05.2015
Kohler F, Rohrbach A
Biophys J. 2015;108(9):2114-25.
Filopodia perform cellular functions such as environmental sensing or cell motility, but also grab for particles and withdraw them leading to an increased efficiency of phagocytic uptake. Remarkably, withdrawal of micron sized particles is also possible without noticeable movements of the filopodia. Here, we demonstrate that polystyrene beads connected by optical tweezers to the ends of adherent filopodia of J774 macrophages, are transported discontinuously towards the cell body. After a typical resting time of 1-2 minutes, the cargo is moved with alternating velocities, force constants and friction constants along the surface of the filopodia. This surfing-like behavior along the filopodium is recorded by a feedback controlled interferometric three-dimensional tracking of the bead motions at 10-100 kHz. We measured transport velocities of up to 120 nm/s and transport forces of about 70pN. Small changes in position, fluctuation width and temporal correlation, which are invisible in conventional microscopy, indicate molecular reorganization of transport relevant proteins in different phases of the entire transport process. A detailed analysis implicates a controlled particle transport with fingerprints of a nanoscale un-/binding behavior. The manipulation and analysis methods presented in our study may be helpful also in other fields of cellular biophysics.
