Thesis-PDF - IAP/TU Wien
Thesis-PDF - IAP/TU Wien
Thesis-PDF - IAP/TU Wien
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4.15), their ends are termed the (-) and the (+) end, and there exist protein<br />
families that can move along the tubes in either of these directions. The two<br />
fascinating protein antagonists are kinesins and dyneins (see Fig. 4.15). These<br />
proteins are capable of moving along a microtubule and, since the tubule has a<br />
defined direction, kinesins always move in the (+) direction and dyneins usually<br />
move in the (-) direction. Even more remarkable is that they are able to move<br />
attached masses. Alone they can move single vesicles, but when acting in unison<br />
it is possible to move direct whole structures!<br />
Together with their motor proteins MTs are essential in molecular cell architecture<br />
for providing transport highways and a mechanism generating relative motion.<br />
Mechanical properties of MT have been described by measuring bending stiffness<br />
with Laser Tweezers, AFM, hydrodynamic flow and buckling in vesicles. Measured<br />
values correspond to Young’s moduli between 1 MP a (rubber) and 7 MP a<br />
(plexiglass). ([102])<br />
Figure 4.14: Schematic drawing of microtubule architecture and how it is<br />
assembled into a flagellar structure (9 doublets of microtubuli forming the<br />
outer wall, a pair is inside). This kind of structure is not only found in alga<br />
but also e.g. as motory flagellum of human sperm. The single microtubule<br />
would have its (-) end on top, its (+) end at the bottom, depending on the<br />
orientation of the heterodimers building the tubule. α−tubulins always face<br />
the (-) end, β−tubulins the (+) end. Image adapted from [102].<br />
Conventional kinesin (or simply ‘kinesin’) is the best known member of the<br />
KinNs (one of the three known families of kinesins)<br />
• Kinesin walks on MT to the (+) end in steps of 8.3 nm per hydrolyzed ATP<br />
(see below). Each second such a motor can complete 100 ATP turnovers and<br />
walk 800nm. A single powerstroke of the motor can generate a force of 6pN.<br />
([103])<br />
• Kinesin is a processive motor, i.e. it does not dissociate from MTs during<br />
walking.<br />
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