Microtubules kinesin movement along

Motion of kinesin heads has been observed by movement of microtubules over biotinylated kinesin fixed to a steptavidin-coated surface,209 by direct observation of fluorescent kinesin moving along microtubules,171 and by optical trap interferometry.210 Kinesin heads move by 8-nm steps, evidently the exact length... 

Certain proteins endow cells with unique capabilities for movement. Cell division, muscle contraction, and cell motility represent some of the ways in which cells execute motion. The contractile and motile proteins underlying these motions share a common property they are filamentous or polymerize to form filaments. Examples include actin and myosin, the filamentous proteins forming the contractile systems of cells, and tubulin, the major component of microtubules (the filaments involved in the mitotic spindle of cell division as well as in flagella and cilia). Another class of proteins involved in movement includes dynein and kinesin, so-called motor proteins that drive the movement of vesicles, granules, and organelles along microtubules serving as established cytoskeletal tracks. ... 

Fig. 19-4).212b However, single kinesin heads, which lack the coiled-coil neck region, have a duty ratio of <0.45. The movement is nonpro-cessive.213 The Ned motor is also nonprocessive.214-216 As mentioned previously, the Ned and kinesin motor domains are at opposite ends of the peptide chain, and the motors move in opposite directions along microtubules.217 218 The critical difference between the two motor molecules was found in the neck domains, which gave rise to differing symmetries in the two heads.219 The latter are shown in Fig. 19-20, in which they have been docked onto the tubulin protofilament structure.

Kinesin hydrolyzes ATP at a rate of approximately 80 molecules per second. Thus, given the step size of 80 A per molecule of ATP, kinesin moves along a microtubule at a speed of 6400 A per second. This rate is considerably slower than the maximum rate for myosin, which moves relative to actin at 80,000 A per second. Recall, however, that myosin movement depends on the independent action of hundreds of different head domains working along the same actin filament, whereas the movement of kinesin is driven by the processive action of kinesin head groups working in pairs. Muscle myosin evolved to maximize the speed of the motion, whereas kinesin functions to achieve steady, but slower, transport in one direction along a filament. 

Figure 34.24. Monitoring Movements Mediated by Kinesin. (A) The movement of beads or vesicles, carried by individual kinesin dimers along a microtubule, can be directly observed. (B) A trace shows the displacement of a bead carried by a kinesin molecule. Multiple steps are taken in the 6-s interval. The average step size is about 8 nm (80 A) [PartB after K. Svoboda, C. F. Schmidt, B. J. Schnapp, and S. M. Block. Nature 365(1993) 721.]...

MAPs include families of motor proteins—kinesins and cytoplasmic dyneins— that use microtubules as a scaffold for transport [reviewed in (48)]. Kinesins and cytoplasmic dyneins convert energy derived from ATP cleavage into movement along the length of the microtubule, mediating the transport of molecules and... 

Homologous switch, converter, and lever arm structures in kinesin are responsible for the movement of kinesin motor proteins along microtubules. The structural basis for dynein movement is unknown because the three-dimensional structure of dynein has not been determined. 

Describe the kinesin-dependent movement of vesicles and organelles along microtubules. Distinguish between the plus and minus ends of a microtubule. 

Howard J. 1996. The movement of kinesin along microtubules. Annu. Rev. Physiol. 58 703-729. 

Fast anterograde transport can reach rates as high as 400 mm/day. It is dependent upon microtubules that provide a track along which the vesicles move. The movement is energy dependent and is mediated by a specific motor protein, kinesin. A similar process is responsible for fast retrograde transport. A second motor protein, dynein, is needed for movement in that direction. A third type of transport process is termed slow axoplasmic transport. It ranges from 0.2 to 5 mm/day and is responsible for the transport of cytoskeletal proteins, the neurofilaments, and microtubules, as well as an assortment of cytoplasmic proteins. 

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