Biology Reference
In-Depth Information
region where the lateral contacts between tubulin dimers are
-
, in contrast to the
a
b
lattice, where the lateral contacts between tubulin dimers are
. The seam
and lattice are thus chemically distinct. Sandblad et al. published binding data that
they interpreted as evidence that EB1 binds strongly to the MT seam and weakly, if at
all, to the lattice (
Sandblad et al., 2006
). However, more recent electron microscopy
and fluorescence microscopy experiments by
Maurer, Fourniol, Bohner, Moores,
and Surrey (2012)
have contradicted Sandblad et al.'s conclusions, providing strong
evidence that EB1 binds to the entire MT and specifically avoids the seam.
How can these reports be reconciled? Using MTBindingSim simulations, it can be
shown that there are other possible interpretations of the Sandblad binding data
(
Fig. 23.3
A) (
Alberico,etal.,2013
). To take a biochemical approach to resolving
-
and
-
a
a
b
b
A
1
0.8
0.6
0.4
Binding data (estimated)
Strong seam-only binding
60% Active protein
Weak lattice binding
100% Active protein
0.2
0
0
5
10
15
20
Total [MT] (
m
M)
B
C
Model: Strong seam binding
Model: First-order binding
1
1
1
m
M EB1
2
m
M EB1
4
m
M EB1
0.8
0.8
0.6
0.6
0.4
0.4
1
m
M EB1
2
m
M EB1
0.2
0.2
4
m
M EB1
0
0
0
5
10
15
20
25
30
0
5
10
15
20
25
30
Total [MT] (
m
M)
Total [MT] (
m
M)
FIGURE 23.3
Does EB1 bind preferentially to the MT seam? (A) Data extracted from
Sandblad et al. (2006)
(green triangles), with overlaid curves corresponding to different binding models as generated
by MTBindingSim. The blue curve shows a simulated curve for strong seam binding
(
M) with 60% active EB1 protein, while the purple curve illustrates the data
expected for weak binding (
K
D
¼
10 M) to the entire MT. These curves show that both binding
models are similarly consistent with the data. (B) Curves from MTBindingSim with strong
seam binding (
0.001
K
D
¼
m
1
M) and weak lattice binding (
1 M) at 1, 2, and 4
M EB1. (C)
K
D
¼
m
K
D
¼
m
Curves fromMTBindingSim with first-order binding to the entire MT lattice (
13
M) at 1,
K
D
¼
m
2, and 4
M EB1.
m
Figures are adapted from
Alberico, et al., (2013)
