Chemistry Reference
In-Depth Information
Figure 3.8 Molecular motor and cytoskeleton
toolbox. Myosin V, cytoplasmic dynein and
conventional kinesin are drawn in surface
rendering approximately to scale with actin and a
microtutuble. Motor catalytic domains are
displayed in blue, mechanical amplifiers (myosin
lever, kinesin neck linker) in light blue, and cargo
attachment domains are shown in purple. Light
and intermediate chains are in green. Dynein is
shown in mixed purple and blue shading to
illustrate the distinct domains that comprise the
motor head. The stalks extending from the ring
bind to microtubules at their globular tips.
Adapted from Vale R.D. (2003), Cell,
112:467
-
480.
Kinesin and dynein are microtubule-based motors that translocate predominantly
toward the plus and minus end of microtubules, respectively. Of the three classic
molecular motors, kinesin is the smallest, having two 40-kDa head domains with a
nucleotide binding fold very similar to the core of the myosin motor domain [57].
The tails dimerize and also carry cargo-binding domains. Like myosin, the large
family of kinesin isoforms are all related by amino acid sequence homology in the
motor domain, but otherwise have diverse structures.
Dynein, at
2MDa, has a more complex head structure containing a ring of
protein domains carrying at least four ATP-binding sites. The motor domain belongs
to the family of ATPases Associated with various cellular Activities (AAA proteins),
including the F1 ATP synthase, heat shock proteins and proteinases [58]. The other
members of this family are oligomers of
6 AAA domain peptides, whereas the
dynein ring contains one large polypeptide with seven domains. A stalk extending
from the ring contains the microtubule binding domain. The N-terminal tails
dimerize and contain complex intermediate and light chains and the cargo-binding
functionality. Flagellar dyneins have one to three heads, whereas cytoplasmic dynein
