Diffusion of Myosin V on Microtubules: A Fine-Tuned Interaction for Which E-Hooks Are Dispensable

Abstract

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.

Tau Protein Diffuses along the Microtubule Lattice

“…Such lattice defects are known to occur in in vitro assembled MT (47). Recently, the actin-based motor myosin-5, which can additionally bind and diffuse along MTs, was reported to occupy two different binding states on MTs: one diffusive and one immobile "trapped" state (32). It was concluded that the immobile trapped state was achieved if, in addition to electrostatic interactions, also non-ionic attraction forces became dominant.…”

“…Our finding that even a randomly selected antibody diffused along MTs supports the idea that one-dimensional diffusion along the microtubule lattice might be a rather common means of dispersion in cells. For such a diffusing molecule, attractive and repulsive charge-charge interactions between the diffusing molecule and the MT need to be well balanced to prevent premature detachment from or immobilization on MTs (24,32). In cells, this balance could be modulated locally to create patterning or asymmetric distributions of proteins (49 -51).…”

“…shown that some MT-binding proteins use the C-terminal peptide of tubulin, the so-called E-hook, for diffusion along the MT lattice (20, 27) whereas others do not (15,32). After enzymatic removal of the tubulin C terminus by subtilisin (Fig.…”

Cytoskeletal crosstalk: when three different personalities team up

“…Their relative contributions seem to depend on external cues such as substrate stiffness [28] and applied mechanical [17] myosin-V [2] kinesin [1] kinesin, dynein [2,53] myosins myosin-V [22] myosin-X [23] MT-tip binding: [5,21] MACF, APC, CLIP-170, CLASP,... MT-lattice binding: [5,18] plectins, ... [15,16] [ 15,16] [9,20]…”

“…Crosstalk between MTs and IFs is also mediated by cross-linkers and motors [2,5], and direct binding in the case of neurofilaments (NFs) [9,20]. Crosstalk between AFs and MTs is mediated by numerous cross-linkers [1,5,21] as well as AF-based [1,22,23] and MT-based motors [1].…”