Biomedical Engineering Reference
In-Depth Information
Table 3.1
Overview of parameters for the different molecular motors kinesin-1, dynein, myosin
V, and myosin VI
Parameter
kinesin-1
dynein
myosin V
myosin VI
7
∗
[
57
], 5
∗
[
5
,
57
]
6
∗
[
72
]
Binding rate
ˀ
[
4
.
1
.
−
−
s
−
1
]
Step size
[
nm
]
8[
91
]
8[
32
]
36 [
21
]
36 [
74
]
Stall force
F
s
[
pN
]
6[
82
,
85
], 5
[
23
], 7 [
19
]
7[
87
]1
.
1[
67
]
1.7 [
21
], 3 [
70
]
2.8 [
78
]
650
∗
[
72
], 700
[
50
]
(Force-free)
velocity
v
1,000 [
82
], 490
[
79
]
400 [
21
], 380 [
1
]
150 [
1
], 291 [
78
]
[
nm
/
s
]
27
∗
[
72
], 0.16
[
68
]
(Force-free)
unbinding rate
0
[
s
−
1
1[
82
], 0.6 [
79
]
0
.
0.48 [
70
], 0
.
3[
1
]
0
.
25 [
1
], 1.3 [
78
]
]
1
∗
[
72
]
4
∗
[
1
]
6
∗
[
1
]
Detachment
force
F
d
3[
82
]
1
.
2
.
[
pN
]
The values marked by an asterisk are inferred indirectly by theoretical modeling of experimental
data
⊧
⊨
v
F
<
0
v
si
(
F
)
≡
v
(
1
−
F
/
F
s
)
0
≤
F
<
F
s
(3.6)
⊩
0
F
≥
F
s
,
see Fig.
3.3
b, but more complicated functional forms and parameterizations can
also be used [
7
]. The force-dependence of the unbinding rate is described by the
exponential form
ʵ
si
(
F
)
≡
ʵ
0
exp
(
|
F
|
/
F
d
).
(3.7)
Note that by using the absolute value of the force, we do not distinguish between dif-
ferent pulling directions. This type of dependence is suggested on theoretical grounds
according to Kramers' rate theory [
53
] and Bell's equation [
6
] and supported by mea-
surements of the force-dependence of the run length [
82
]. The force-dependence of
the unbinding rate is currently revisited by several labs for different types of motors.
Deviations from this exponential increase have recently been reported for dynein
motors, with an exponential increase for small forces but catch-bond-like behavior,
i.e., a decrease in the unbinding rate, for forces around the stall force [
55
,
59
].
Since it is difficult to measure the binding rate
directly, its value has been
determined by fitting theoretical models to experimental data. In this way, a binding
rate
ˀ
7s
−
1
is obtained from an experiment where kinesin-1 motors extract
membrane nanotubes from vesicles [
57
]. A similar value has been reported in a study
fitting the run length distribution of beads transported by several kinesin-1 motors
[
5
]. For other types of motors, most of the parameters have also been determined
experimentally; the corresponding parameter values are summarized in Table
3.1
.
The simple stochastic stepper description of a single motor incorporates those
properties of single motors that are relevant for large-scale cargo transport. Further-
more, the theoretical framework described here can easily be extended, for example,
ˀ
4
.
Search WWH ::
Custom Search