Our current efforts aim at a detailed mechanistic understanding of the Myosin-driven transport of melanosomes in Xenopus melanophores. It was suggested that Myosin V transport activity is only required during the dispersion process and is dispensable during melanosome aggregation. By establishing the melanosome transport by Myosin V on actin filaments in vitro, we want to shed light on the regulatory mechanism governing Myosin V activity.
Diffusion of Myosin V on Microtubules.
Organelle transport in eukaryotes employs both microtubule and actin tracks to deliver cargo effectively to their destinations, but the question of how the two systems cooperate is still largely unanswered. Recently, in vitro studies revealed that the actin-based processive motor myosin V also binds to, and diffuses along microtubules. This biophysical trick enables cells to exploit both tracks for the same transport process without switching motors. The detailed mechanisms underlying this behavior remain to be solved. By means of single molecule Total Internal Reflection Microscopy (TIRFM), we show here that electrostatic tethering between the positively charged loop 2 and the negatively charged C-terminal E-hooks of microtubules is dispensable. Furthermore, our data indicate that in addition to charge-charge interactions, other interaction forces such as non-ionic attraction might account for myosin V diffusion. These findings provide evidence for a novel way of myosin tethering to microtubules that does not interfere with other E-hook-dependent processes. pdf