Chemistry Reference
In-Depth Information
Figure 5.5 Single-molecule dynamics of the movements of
NGF/NGFR complexes. (A) A representative trajectory of a
Cy3
-
NGF receptor complex over 7.6 s showing reversible
transitions inmobile and immobile behavior. Immobile segments
are circled. Scale bar, 1 mm. (B) Signals from an NGF/NGFR
complex do not flow to Raf1 continually but at discrete times and
space. See text for details.
1 and 1.5 s, respectively. Single exponential distributions suggest that the motional
modes switch in single rate-limiting steps.
During the immobilization period, the NGF/NGFR complex often formed clus-
ters. The clustering continued throughout the immobile phase. Since the formation
of simple clusters of this size cannot reduce the membrane protein diffusion
coef
cient signi
cantly, the complex is more likely to consist of a transient molecular
complex including cytoplasmic cell signaling proteins. It is also possible that some of
the elements in the complex associated with the membrane skeleton.
TrkA is an NGF receptor that belongs to the RTK superfamily. Treatment of cells
with a trkA-speci
c kinase inhibitor, k252a, decreased the population of molecules
which showed immobilization. However, for the remaining population of molecules
which showed immobilization, the lifetimes of both the mobile and immobile phase
