Thesis-PDF - IAP/TU Wien

• It possesses a hand-over-hand (h-o-h) moving mechanism: its two heads pass
over one another when the protein moves along the tube. In this way it is
similar to the human walking style. (see Fig. 4.15, [104])
• The theoretical prediction of this model predicted a 16.6 nm step size per
head.
• By labeling one head with a fluorescent dye, the average step size of one
single head was shown to be 17.3nm as predicted by the h-o-h model (another
model, the inchworm model in contrast predicted only 8 nm). ([104])
The movement mechanism of dyneins is less well understood.
ATP
In order to move along a MT a motor protein has to dispose of enough energy. The
cell provides this energy to many of its subsystems through the protein adenosine
triphosphate (ATP). ATP is regarded as the main energy currency of biological
systems. The ATP molecule owes much of its energy to the terminal three phosphate
ions attached to an adenosine base. When the third phosphate group of
ATP is split off by hydrolysis, free energy of a value of about 7.3 kcal (the exact
amount depending on various other conditions) per mole is released.
AT P + H 2 O ⇒ ADP + P i
Adenosine diphosphate (ADP) and inorganic phosphate (P i ) are left as the
products. The released energy can be used to drive biological processes.
• ATP is the main energy currency of the cell, providing the energy for most
of the energy-consuming activities of the cell.
• It is used as monomer in the synthesis of RNA and, after conversion to
deoxyATP (dATP), DNA.
• Necessary for the regulation of many biochemical pathways.
ADP and the phosphate group on the other hand are recombined to form ATP
again by a very efficient enzyme motor assembly called the F 0 F 1 -ATP synthase
protein (F 0 F 1 -ATPase). This energy cycle, the splitting of the phosphate group
and the reattachment by ATPase, is reversible and highly efficient. ATP synthase
can be found inside the mitochondria of animal cells, in plant chloroplasts, in
bacteria, and some other organisms.
Thus the energy for dynein and kinesin movement comes from the splitting
of ATP molecules. Through regulation of ATP accessibility their activity can be
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