Chemistry Reference
In-Depth Information
Figure 7.4 Single-molecule force spectroscopy
on cell surface receptors. (A) Different strategies
of functionalization of AFM probes and solid
supports for investigating ligand
shaded area represents de-adhesion between the
cell and the substrate, and F
cell
is the detachment
force. In trace 2, T-cells were stimulated with
Mg
2þ
/EGTA, which induced tighter adherence
to ICAM-1 than that in resting cells. Arrows
indicate single rupture events. In trace 3,
addition of antibodies against either LFA-1 or
ICAM-1 inhibited the adhesion (adapted
from [138]). (D) Dynamic force spectrum of LFA-
1/ICAM-1 interactions. Two loading regimes in
the average unbinding forces were observed. For
details on the extracted Bell model parameters
(see Table 2; adapted from [138]).
receptor
interactions in living cells (see text for details).
(B) Optical micrograph of a T-cell attached to the
tip of an AFM cantilever (taken from [138]). (C)
Force-displacement measurements between
LFA-1 expressed on the surface of T-cells and
immobilized ICAM-1. LFA-1/ICAM-1
interactions are important for leukocyte
adhesion. Traces were acquired using a
retraction speed of 2
-
ms
1
. In trace 1, the
m
surface, (iii) cells are attached to both the cantilever and the supporting surface for
cell
-
cell contact experiments. Since bacterial cells cannot spread on solid surfaces,
firm attachments must be achieved in order to carry out imaging and force
experiments.
The general procedure for force spectroscopy consists of measuring the unbinding
forces of single ligand
-
receptor complexes in force
-
distance cycles recorded at
different loading rates. Figure 7.4C shows single molecular recognition events in
the force curve. Since mechanical breaking is a stochastic process, several hundred
force curves should be recorded to extract a statistically relevant value of the
