Thesis-PDF - IAP/TU Wien

Figure 4.15: Kinesin and dynein and their direction of propagation along
a microtubule. Kinesin has a remarkable way of moving by using the handsover-hands
method. Its two heads pass over another when the protein moves
along the tube. In this way it is similar to the human walking style, putting
one foot in front of the other. Scale bar is 50nm. Image adapted from [102].
precisely regulated, such that a complex concerted action like euglenoid movement
is made possible.
Besides providing the pellicle with dynamic properties one major area of microtubule
usage can be found in the flagellum. The core structure of Euglena’s
flagellum consists of nine outer doublets of microtubli and one inner doublet. The
cross section of such an arrangement shows that each outer doublet has a dynein
protein attached to it, enabling the flagellum to actively slide within its shaft. This
basic mechanism is responsible for the typical flagellar ondulatory movement.
A very interesting fact about the Euglena pellicular strip is their assembly
process. Instead of being transferred and attached in part to the plasma membrane,
they are assembled molecule by molecule. The location where the individual
proteins bind is directed by special binding sites spread on the inner side of
the plasma membrane. The membrane skeleton (pellicle) of Euglena is primarily
assembled from a 80 kDa 12 membrane skeletal protein binding to the plasma
membrane through noncovalent interactions with a small cytoplasmic domain of
the plasma-membrane protein IP39. ([101])
The pellicle, or membrane skeleton, underlying the plasma membrane plays a
12 A dalton (Da or D) is a unit of mass, equivalent to the unified atomic mass unit (u). It is
defined to be one twelfth of the mass of an unbound atom of the carbon-12 nuclide, at rest and
in its ground state. 1kDa = 1000 Da. E.g. a caffeine molecule has a mass of 194 Da.
57