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Introduction
Kinesins are proteins which serve as molecular motors for the directional transport of various cargos (Hirokawa et al. 10: 682-696). They perform this important function using different mechanisms to recognize, bind, determine the direction of transport and unload the cargos with an energy efficiency which can exceed 50%, thereby equipping them to play important roles intracellularly in the transport of organelles and vesicles, in biosensing as well as in the development of other bioengineering solutions (Agarwal 11; Hirokawa and Takemura 301: 50–9; Hirokawa et al. 10: 682-696; Lin et al. 8: 1041–6). Kinesin transports its cargoes along microtubule (MT) filaments and are powered by the hydrolysis of adenosine triphosphate (ATP), consuming one ATP molecule for every step (Coy, Wagenbach and Howard 274: 3667–3671). Scientists have designed in vitro assays called “motility assays” to study kinesins and its cytoskeletal filament (microtubules) in a synthetic environment. Below is a comparison of the performance of kinesin expressed in insect systems to those expressed in E. coli in motility gliding assays.
Velocity
Microtubules propelled by kinesin expressed in insect systems have a higher velocity than those propelled by kinesin expressed in E. coli. Korten et al. who evaluated the frame-to-frame velocities of microtubules expressed in insect systems and those expressed in bacteria discovered that kinesin expressed in bacteria had a median velocity of 755nm/s and a 25–75 percentile velocity of 461–825nm/s while those expressed in insects were significantly faster (p<0.001) with a median velocity of 844nm/s and a 25–75 percentile of 771–898nm/s, using Wilcoxon rank sum test (15:64). This result also tallies with that reported by Agayan et al. 29: 2265–2272.
Kinesin expressed in E. coli does not persist in motion for as long as those expressed in insects. In a research carried out by Korten et al. (15:65), the median velocity of kinesin expressed in bacteria was observed to be constant for only 40minutes after which it was observed to decline rapidly with termination of all microtubule movement occurring after 2hours. In contrast, kinesin expressed in insect cells were reported to still be active for more than 24 hours (26hours), expressing a slight increase in velocity initially after which the increased velocity remained constant. Microtubule stopping has been attributed to the antagonistic effect of non-motile motor proteins on motile motors (Scharrel et al. 107: 365 - 372). Increased stopping seen in microtubules propelled by kinesin expressed in bacteria has been postulated to be caused by truncated kinesin-1 proteins resulting from impaired heterodimers which is as a result of premature termination of translation in the expression system of the bacteria (Korten et al. 15: 65–66; Kurland and Gallant 7: 489 – 493).
Length of microtubule propelled
Regarding length, microtubules propelled by kinesin expressed in E. coli break more than those expressed in insect cells. This is seen from research carried out by Korten et al. who counted the number of microtubules per field of view in an experiment and observed that for kinesin expressed in bacteria, the number of microtubules increased rapidly within the first four hours and remained constant at 117+8 microtubules/field of view while for kinesin expressed in insects, the number of microtubules remained constant at 26+5 per field of view (15: 66). This increase in number of microtubules per field of view observed in kinesin expressed in bacteria can only be as a result of breakage since free microtubules in the solution were washed off at the commencement of the experiment (Korten et al. 15: 66). Microtubule breakage has been explained by the same researchers to likely result when the forces exerted by moving and stopping motors exceed the microtubule load limit. This explains the absence of microtubule breakage in kinesin expressed in insects which possess less stopping motors as evidenced by few microtubules stopping, unlike kinesin expressed in bacteria which had more stopped microtubules (as mentioned above) (Korten et al. 15: 66).
Guiding in nanostructures
Furthermore, kinesin expressed in insects are better guided in nanostructures with less loss of microtubules than kinesin expressed in E. coli. Test of how kinesins (both those expressed in insect cells and those expressed in E. coli) affect guiding at walls using lithographically defined nanostructures reveal an overall guiding efficiency of 95+1.2% for kinesin expressed in insect cells as against 61+3.8% for kinesin expressed in bacteria (Korten et al. 15: 67). This high guiding efficiency seen in kinesin expressed in insect cells does not only exceed that observed in bacteria but most other gliding efficiencies for microtubules so far reported (Hiratsuka et al. 81: 1555–1561; Clemmens et al. 19: 10967–10974; Van den Heuvel et al.5: 1117-1122).
Conclusion
The improved performance of kinesin expressed in insect systems over those expressed in E. coli (in terms of velocity, persistence in motion, length of microtubule propelled and guiding in nanostructures) makes it a more suitable motor protein for use in nanotechnological applications.
Works Cited
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Scharrel, L., Ma, R., Schneider, R., Jülicher, F. and Diez, S. “Multimotor Transport in a System of Active and Inactive Kinesin-1 Motors,” Biophys. J. 107.2 (2014): 365–372. Web. 24 July. 2016.
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Van den Heuvel, M.G.L., Butcher, C.T. Smeets, R.M.M., Diez, S. and Dekker, C. “High Rectifying Efficiencies of Microtubule Motility on Kinesin-Coated Gold Nanostructures,” Nano Lett., 5.6 (2005): 1117–1122. Web. 24 July. 2016.
