Biomedical Engineering Reference
In-Depth Information
6
Con A coated bead
BSA coated bead
5
4
3
2
1
0
0
5
10
15
20
25
30
35
40
45
50
55
Time (s)
Fig. 14.14.
The time-dependence of the relative amplitude of a polystyrene bead
(diameter = 2.83
µ
m) executing optical forced oscillation at 50 Hz in the vicinity
of a CHO cell. The experimental data for ConA-coated bead are denoted by solid
squares and the data for a BSA-coated bead are denoted by “*”
for the lectin-glycoprotein interaction. When the CHO cell was treated with
lantrunculin A, a drug that is known to destroy the cytoskeleton of the cell,
the oscillation amplitude increased with time, indicating the softening of the
cellular membrane, until a steady state with a smaller force constant was
reached. The steady state value of the force constant depended on the drug
concentration.
As an illustrative example, the time dependence of the relative amplitude
of a polystyrene bead (diameter = 2.83
m) oscillating at 50 Hz in the vicinity
of a Chinese hamster ovary cell is depicted in Fig. 14.14 for the case of a BSA-
coated bead and that of a ConA-coated bead. The decay of the oscillation
amplitude in the case of the ConA-coated bead is a manifestation of the
interaction of ConA protein with the glycol-protein on the cellular membrane
of the CHO cell.
µ
14.4.2 Protein-DNA Interaction
The interaction of proteins with DNA plays a pivotal role on a number of
important biological processes, including DNA repair, replication, recombina-
tion, and segregation. Many different proteins can be used as models for such
investigations. For example, one can optically trap-and-stretch a segment of
dsDNA to analyze the dynamics of homologous DNA search and strand ex-
change reaction mediated by RecA protein.
In the study of protein-DNA interaction, micron-size polystyrene beads
are often attached to the ends of each DNA sample, one at each end, to serve
as handles for optical tweezers to trap and stretch the DNA sample between
the beads. A schematic illustration of a dsDNA segment stretched between
a fixed (large) bead (with diameter
∼
20
m) and an optically trapped small
µ
