Biology Reference
In-Depth Information
techniques enable us to detect richer force-dependent behaviours such as
those observed in catch bonds.
In practice, there are still some points in force measurements of adhesion
strength that would require further study. For example, it is still under debate
the possible effect of the probe stiffness in the measured forces.
36,67,99
This
question is especially relevant in cell adhesion, since cells have the capacity
of changing their mechanical properties in response to external signals.
39,100
Additional open questions include the effect of possible rebinding during
pulling and the consequence of multiple bonds in the averaged rupture
forces.
99,101
Although we have focused on the dissociation kinetics of cell
adhesion bonds, the association kinetics might be even more relevant in
some cases, such as in leukocyte binding to the endothelium. It has been
reported that the association kinetics of biomolecules immobilized on a
surface (2D), and even more on two opposing surfaces, vary signiicantly
from those measured in 3D.
102
Some approaches have been already applied
to determine the 2D association rates, using AFM and other force techniques,
but an established method is still lacking.
102-105
Regarding the biological relevance of force measurements using AFM,
although it is useful to describe a biological interaction in terms of a well-
deined energy landscape, it does not provide much information about the
nature of the interaction itself, neither about its molecular determinants.
Addressing this question requires complementary studies using molecular
dynamic simulations, speciic monoclonal antibodies or site-directed
mutagenesis to be combined with force measurements. The molecular basis
of the adhesion strength of some adhesion receptors have been studied
using various force techniques combined with site-directed mutations or
deletion constructs showing the contribution of speciic amino acids to the
shape of the energy landscape.
33,37,52,62,106
Molecular dynamics simulations
provided an irreplaceable and valuable tool to determine the precise
dissociation mechanism of molecular interactions in the early stages of
force measurements and continue to shed light to the ield.
57,107
An interesting
question that would require further attention is the possible memory of
adhesion receptors.
108
An important and not very well-studied interaction relevant for cell
adhesion is the binding between the cytoplasmic domains of CAMs and
the proteins that mediate linking with the cytoskeleton. Although some
approaches have been described using other techniques,
40
it is still a challenge
to be able to measure the interaction forces in living cells in a controlled and
speciic manner.
The inal goal of single-molecule studies is to understand how cell
adhesion works. To describe whole cell adhesion, we will require appropriate
Search WWH ::
Custom Search