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Cooperative protofilament switching emerges from inter-motor interference in multiple-motor transport.

Ando D, Mattson MK, Xu J, Gopinathan A - Sci Rep (2014)

Bottom Line: Within living cells, the transport of cargo is accomplished by groups of molecular motors.In contrast to kinesin's low sidestepping frequency when present as a single motor, with exactly two kinesins per cargo, we observed substantial motion perpendicular to the microtubule.Our model captures a surface-associated mode of kinesin, which is only accessible via inter-motor interference in groups, in which kinesin diffuses along the microtubule surface and rapidly "hops" between protofilaments without dissociating from the microtubule.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, University of California, Merced, CA, USA.

ABSTRACT
Within living cells, the transport of cargo is accomplished by groups of molecular motors. Such collective transport could utilize mechanisms which emerge from inter-motor interactions in ways that are yet to be fully understood. Here we combined experimental measurements of two-kinesin transport with a theoretical framework to investigate the functional ramifications of inter-motor interactions on individual motor function and collective cargo transport. In contrast to kinesin's low sidestepping frequency when present as a single motor, with exactly two kinesins per cargo, we observed substantial motion perpendicular to the microtubule. Our model captures a surface-associated mode of kinesin, which is only accessible via inter-motor interference in groups, in which kinesin diffuses along the microtubule surface and rapidly "hops" between protofilaments without dissociating from the microtubule. Critically, each kinesin transitions dynamically between the active stepping mode and this weak surface-associated mode enhancing local exploration of the microtubule surface, possibly enabling cellular cargos to overcome macromolecular crowding and to navigate obstacles along microtubule tracks without sacrificing overall travel distance.

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Single- and Two-kinesin motor transverse displacement measurements.(a) Histograms of the transverse displacement of cargos transported by one (left) or two (right) kinesins at the indicated ATP concentrations. DTDs occur at 10 and 20 µM ATP for two-kinesin transport. (b) Top: Histogram of transverse cargo displacement at 10 µM ATP for two motor traces with travel distance >5 µm. Using a binning histogram density of 30 bins per 40 nm, the leftmost sidestep peak is located at -53.3 nm and the remaining sidestep peak on the left side is located at -29.8 nm. The rightmost sidestep peak is located at 53.3 nm and the remaining right single sidestep is located at 26.6 nm. We find that “left” and “right” DTDs occur with roughly equal probability (49% vs 51%). Bottom: Same as (Top) except depicting traces with travel distances <5 µm. The sum of these two histograms is equal to the histogram of DTDs of two-kinesin transport at 10 µM ATP. A sum of five gaussians approximates the two-motor (>5 µm travel) transverse motion histogram well (Top), while the histogram of DTDs for the shorter traces (Bottom) was well approximated by a single gaussian. (c) Two-motor traces at 10 µM ATP separate into two groups. One group (boxed in red) has a low standard deviation in its transverse displacement size of 46 nm on average, has a high processivity (>5 µm), and a low velocity of 109 nm/s on average. Another group (boxed in blue) has traces with a travel distance of >5 µm, a high standard deviation in its transverse displacement size of 62 nm on average, and a higher velocity of 187 nm/s on average.
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f1: Single- and Two-kinesin motor transverse displacement measurements.(a) Histograms of the transverse displacement of cargos transported by one (left) or two (right) kinesins at the indicated ATP concentrations. DTDs occur at 10 and 20 µM ATP for two-kinesin transport. (b) Top: Histogram of transverse cargo displacement at 10 µM ATP for two motor traces with travel distance >5 µm. Using a binning histogram density of 30 bins per 40 nm, the leftmost sidestep peak is located at -53.3 nm and the remaining sidestep peak on the left side is located at -29.8 nm. The rightmost sidestep peak is located at 53.3 nm and the remaining right single sidestep is located at 26.6 nm. We find that “left” and “right” DTDs occur with roughly equal probability (49% vs 51%). Bottom: Same as (Top) except depicting traces with travel distances <5 µm. The sum of these two histograms is equal to the histogram of DTDs of two-kinesin transport at 10 µM ATP. A sum of five gaussians approximates the two-motor (>5 µm travel) transverse motion histogram well (Top), while the histogram of DTDs for the shorter traces (Bottom) was well approximated by a single gaussian. (c) Two-motor traces at 10 µM ATP separate into two groups. One group (boxed in red) has a low standard deviation in its transverse displacement size of 46 nm on average, has a high processivity (>5 µm), and a low velocity of 109 nm/s on average. Another group (boxed in blue) has traces with a travel distance of >5 µm, a high standard deviation in its transverse displacement size of 62 nm on average, and a higher velocity of 187 nm/s on average.

Mentions: To probe the functional interactions between two kinesin motors transporting the same cargo, we focused on the changes in cargo position in the direction transverse to the microtubule between subsequent recording frames (33.3 ms temporal resolution). We observed considerable changes in the transverse displacement of two-motor cargos with reducing ATP concentration, but not for single-motor cargos (Fig. 1A, Supplementary Discussion Fig. 1). Specifically, we observed symmetric transverse displacement for both one- and two-motor cargos (Fig. 1, and representative traces in Supplementary Discussion Fig. 1), indicating that cargo motion is not biased in either direction perpendicular to the microtubule. However, with reducing ATP concentration (10 and 20 µM), distinct peaks emerged within the cumulative distributions of the two-motor transverse displacement due to what we term discrete transverse displacements (DTDs). The width and variance of these DTD peaks were substantially smaller than those of the one-motor distribution (>10-fold, Fig. 1A, Supplementary Discussion Fig. 1). The narrow DTD peak width suggests that these peaks correspond to a geometry in which the cargo is linked to the microtubule by two motors, thus increasing the effective linkage stiffness and reducing the effect of thermal noise on cargo position.


Cooperative protofilament switching emerges from inter-motor interference in multiple-motor transport.

Ando D, Mattson MK, Xu J, Gopinathan A - Sci Rep (2014)

Single- and Two-kinesin motor transverse displacement measurements.(a) Histograms of the transverse displacement of cargos transported by one (left) or two (right) kinesins at the indicated ATP concentrations. DTDs occur at 10 and 20 µM ATP for two-kinesin transport. (b) Top: Histogram of transverse cargo displacement at 10 µM ATP for two motor traces with travel distance >5 µm. Using a binning histogram density of 30 bins per 40 nm, the leftmost sidestep peak is located at -53.3 nm and the remaining sidestep peak on the left side is located at -29.8 nm. The rightmost sidestep peak is located at 53.3 nm and the remaining right single sidestep is located at 26.6 nm. We find that “left” and “right” DTDs occur with roughly equal probability (49% vs 51%). Bottom: Same as (Top) except depicting traces with travel distances <5 µm. The sum of these two histograms is equal to the histogram of DTDs of two-kinesin transport at 10 µM ATP. A sum of five gaussians approximates the two-motor (>5 µm travel) transverse motion histogram well (Top), while the histogram of DTDs for the shorter traces (Bottom) was well approximated by a single gaussian. (c) Two-motor traces at 10 µM ATP separate into two groups. One group (boxed in red) has a low standard deviation in its transverse displacement size of 46 nm on average, has a high processivity (>5 µm), and a low velocity of 109 nm/s on average. Another group (boxed in blue) has traces with a travel distance of >5 µm, a high standard deviation in its transverse displacement size of 62 nm on average, and a higher velocity of 187 nm/s on average.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4248269&req=5

f1: Single- and Two-kinesin motor transverse displacement measurements.(a) Histograms of the transverse displacement of cargos transported by one (left) or two (right) kinesins at the indicated ATP concentrations. DTDs occur at 10 and 20 µM ATP for two-kinesin transport. (b) Top: Histogram of transverse cargo displacement at 10 µM ATP for two motor traces with travel distance >5 µm. Using a binning histogram density of 30 bins per 40 nm, the leftmost sidestep peak is located at -53.3 nm and the remaining sidestep peak on the left side is located at -29.8 nm. The rightmost sidestep peak is located at 53.3 nm and the remaining right single sidestep is located at 26.6 nm. We find that “left” and “right” DTDs occur with roughly equal probability (49% vs 51%). Bottom: Same as (Top) except depicting traces with travel distances <5 µm. The sum of these two histograms is equal to the histogram of DTDs of two-kinesin transport at 10 µM ATP. A sum of five gaussians approximates the two-motor (>5 µm travel) transverse motion histogram well (Top), while the histogram of DTDs for the shorter traces (Bottom) was well approximated by a single gaussian. (c) Two-motor traces at 10 µM ATP separate into two groups. One group (boxed in red) has a low standard deviation in its transverse displacement size of 46 nm on average, has a high processivity (>5 µm), and a low velocity of 109 nm/s on average. Another group (boxed in blue) has traces with a travel distance of >5 µm, a high standard deviation in its transverse displacement size of 62 nm on average, and a higher velocity of 187 nm/s on average.
Mentions: To probe the functional interactions between two kinesin motors transporting the same cargo, we focused on the changes in cargo position in the direction transverse to the microtubule between subsequent recording frames (33.3 ms temporal resolution). We observed considerable changes in the transverse displacement of two-motor cargos with reducing ATP concentration, but not for single-motor cargos (Fig. 1A, Supplementary Discussion Fig. 1). Specifically, we observed symmetric transverse displacement for both one- and two-motor cargos (Fig. 1, and representative traces in Supplementary Discussion Fig. 1), indicating that cargo motion is not biased in either direction perpendicular to the microtubule. However, with reducing ATP concentration (10 and 20 µM), distinct peaks emerged within the cumulative distributions of the two-motor transverse displacement due to what we term discrete transverse displacements (DTDs). The width and variance of these DTD peaks were substantially smaller than those of the one-motor distribution (>10-fold, Fig. 1A, Supplementary Discussion Fig. 1). The narrow DTD peak width suggests that these peaks correspond to a geometry in which the cargo is linked to the microtubule by two motors, thus increasing the effective linkage stiffness and reducing the effect of thermal noise on cargo position.

Bottom Line: Within living cells, the transport of cargo is accomplished by groups of molecular motors.In contrast to kinesin's low sidestepping frequency when present as a single motor, with exactly two kinesins per cargo, we observed substantial motion perpendicular to the microtubule.Our model captures a surface-associated mode of kinesin, which is only accessible via inter-motor interference in groups, in which kinesin diffuses along the microtubule surface and rapidly "hops" between protofilaments without dissociating from the microtubule.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, University of California, Merced, CA, USA.

ABSTRACT
Within living cells, the transport of cargo is accomplished by groups of molecular motors. Such collective transport could utilize mechanisms which emerge from inter-motor interactions in ways that are yet to be fully understood. Here we combined experimental measurements of two-kinesin transport with a theoretical framework to investigate the functional ramifications of inter-motor interactions on individual motor function and collective cargo transport. In contrast to kinesin's low sidestepping frequency when present as a single motor, with exactly two kinesins per cargo, we observed substantial motion perpendicular to the microtubule. Our model captures a surface-associated mode of kinesin, which is only accessible via inter-motor interference in groups, in which kinesin diffuses along the microtubule surface and rapidly "hops" between protofilaments without dissociating from the microtubule. Critically, each kinesin transitions dynamically between the active stepping mode and this weak surface-associated mode enhancing local exploration of the microtubule surface, possibly enabling cellular cargos to overcome macromolecular crowding and to navigate obstacles along microtubule tracks without sacrificing overall travel distance.

Show MeSH
Related in: MedlinePlus