properties of motors within these com-
plexes, and their collective dynamic
Current studies of collective motor
functions have been confounded by the
fact that the number and spatial arrange-
ment of motors on a cargo are unknown
in most assays and must be inferred
from analyses of cargo motions. The
combination of these experimental
deficiencies and the inherent complex-
ities of collective motor behaviors have
left many aspects of multiple motor
dynamics poorly defined and contro-
versial. To address these challenges,
several groups have developed meth-
ods to generate organized motor com-
plexes using molecular scaffolds com-
posed of protein-based polymers, lin-
ear DNA duplexes, and other biomac-
romolecules (7–9). These approaches
provide important abilities to quantify
differences between single and multi-
ple motor run lengths, velocities, and
force production. However, they have
allowed small motor complexes to be
prepared that typically only contain two
identical motors. Derr et al. have over-
come this limitation by engineering
DNA scaffolds, called DNA origami,
in order to create motor complexes that
better reflect the size and complexity of the
motor systems responsible for the transport of
natural cargos. The DNA origami is formed
by folding a long viral single-stranded DNA
strand into an organized structure by anneal-
ing this strand with collections of small oli-
gonucleotides called “staple strands,” which
hybridize to different regions of the viral
DNA (10). This method allows long molecu-
lar scaffolds to be synthesized whose persis-
tence length can far exceed that of a single
DNA duplex because multiple duplexes can
be tied together. The staple strands can also
be extended from the structure and used to
specify sites where DNA-tagged motors and
fluorescent labeling strands are linked to the
scaffold. The resulting ability to program the
number, sequence, and spatial presentation
of these handles allows near-arbitrarily com-
plex, three-dimensional scaffolds to be pre-
pared that can template the self-assembly of
multiple protein systems containing collec-
tions of different proteins.
The development of recombinant yeast
dynein expression constructs that can be
outfitted with oligonucleotides also pro-
vided Derr et al. with new opportunities to
engineer motor complexes containing oppo-
sitely directed kinesin and dynein motors
and then examine how these microtubule
Cytoskeletal transport championships
Motor binding stepping and detachment
the ability of multiple kinesins to
cooperate productively by sharing
their applied loads (see the figure).
The present dynein motors pos-
sess much higher filament affini-
ties than kinesin and advance at
much lower rates, which appears
to relieve these constraints,
yielding net minus end–directed
motions even at low dynein-to-
The ability to controllably tune
the motor ratios will likely shed
light on intracellular transport reg-
ulatory mechanisms. The domi-
nant role of high-affinity motors
in the present ensembles suggests
that controlling their number and
activities will be particularly influ-
ential to tug-of-war competitions.
Nevertheless, the mechanochemi-
cal properties of motors can vary
appreciably depending on their
structure and association with spe-
cific accessory factors, indicating
that characteristically different col-
lective responses can potentially be
produced by other motor systems.
Analogously rich collective behav-
iors are known to occur when non-
motile proteins interact in groups
and operate as integrated biosynthetic facto-
ries and signaling complexes (14, 15). Conse-
quently, the ability to make use of DNA self-
assembly techniques to engineer organized
multiple protein assemblies and determinis-
tically modulate their composition will likely
constitute an important new approach to dis-
secting the functions of various integrated
macromolecular systems of proteins.
Oppositely directed motors compete in a tug-of-war. Many cargos are
outfitted with different types of antagonistic cytoskeletal motors in cells
and move bidirectionally along cytoskeletal filaments. Using molecular
scaffolds call DNA origami to generate organized multiple motor com-
plexes, Derr et al. show that teams of yeast dyneins tend to win tug-of-
war competitions with multiple kinesins. Despite its lower stalling force,
dynein’s high microtubule affinity tips the scale in the dynein team’s
favor because this property allows more dyneins to remain engaged dur-
ing a tug-of-war against a team of kinesins, which tend to use only a
small fraction of their motors during the competition.
motors compete to control the direction of
cargo motion. Single kinesin motors move
processively toward the plus end of micro-
tubules and can produce forces up to 7 pN.
Yeast dynein is a minus end–directed motor
and has been found to stall at somewhat
smaller forces (5 pN) (11). One may there-
fore expect that teams of kinesins would
prevail over similar-sized teams of dyneins
during a molecular tug-of-war. However,
Derr et al. found that collections of dyneins
tended to win this competition, except in
extreme cases where the number of kines-
ins far outweighed the number of dyneins in
a complex. These results show that factors
other than a motor’s stalling force can play
key roles determining how motors cooper-
ate in groups. They are also consistent with
recent optical trapping studies that have
suggested that teams of kinesins use only
a small fraction of their motors at a time
when transporting cargos against opposing
loads on average (9, 12). This weak coop-
erative response has been attributed to kine-
sin’s relatively high stepping rate under
load and large stalling force relative to its
critical detachment force (8, 13). Although
these properties allow kinesin to function
efficiently as single motor molecules, they
can produce kinetic constraints that limit
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