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Engineering Approaches to Biomolecular Motors: From in vitro to in vivo Thursday Speaker Abstracts
21
Translational and Rotational Motion of Coupled Motor Proteins
Andrej Vilfan
.
J. Stefan Institute, Ljubljana, Slovenia.
The dynamics of groups of coupled motor proteins is interesting both due to its relevance for
cargo transport in vivo and as a possibility to study motor features that are not accessible in
single molecule experiments. But the relationship between collective properties of motor
ensembles and those of individual motors is often not straightforward.
We will first look at pairs of myosin-V motors, coupled through an elastic linkage. The
randomness of their motion leads to a buildup of tension, which in turn slows the pair down. It
also leads to an increased detachment rate of the motors. The run length of a pair is longer than
that of a single motor, but the enhancement is surprisingly small (~50%). This has important
implications for the nature of detachment events.
In the second part we investigate the working stroke of kinesin-14 (ncd) motors based on
ensemble measurements in a gliding motility assay with simultaneous recording of translational
and rotational motion of microtubules as a function of ATP and ADP concentrations. The
measured velocity is zero below a threshold [ATP] and increases abruptly above that
concentration. The rotational pitch also depends on the ATP concentration and is shortest at low
[ATP]. Combined with a simple mechanical model, both findings indicate that the main power
stroke of kinesin-14 takes place after ATP binding and that each step also comprises a small off-
axis component. By fitting the measured data with the model solution we show that the working
stroke starts with a small movement of the motor's stalk in lateral direction when ADP is
released. When ATP binds it is followed by a second, main stroke with a primarily longitudinal
direction and a small lateral component in a direction that is opposite to the initial lateral step.