Biomedical Engineering Reference
In-Depth Information
Figure 4.3.
Microtubule end-binding proteins. Specialized proteins interact with
the dynamic ends of microtubules
in vivo
to control microtubule dynamics, deliver
cargo, or mediate interactions with the cell cortex. (a) Artist impression of the
protein complexity at microtubule ends in cells. (b) Fluorescent antibody staining
of EB1, a catastrophe suppressing end-binding protein in mammalian cells. Image
of COS-7 cell courtesy of Dr. Anna Akhmanova. (c) Life imaging using fluorescent
protein (FP) labeling of two different end binding proteins, tip1p and mal3p, in
interphase fission yeast cells. Images taken every 10.4 sec (top) and 4 sec (bottom);
courtesy of Dr. Damian Brunner. When microtubules reach the cell ends, Mal3p
disappears before catastrophes occur. (See color insert.)
4.3 Microtubule Assembly Forces in Theory
The notion that the assembly (and disassembly) of cytoskeletal filaments can
provide a useful source of energy for mechanical force generation was first put
forward in the 1980s by Terrell Hill [17]. Fueled overall by the consumption
of GTP, both the assembly and disassembly of microtubules are energetically
favorable processes that are available in principle as a source of energy to
perform work [2]. Depending on the exact conditions, the gain in free en-
ergy (
ΔG
) connected with the addition of a single GTP-tubulin dimer to a
growing microtubule is on the order of 5
−
10
k
B
T
, where
k
B
is Boltzmann's
