Biomedical Engineering Reference
In-Depth Information
conformation, as Stage (e). Then, the unit returns to the tightly binding state
via an initial binding state (f). An antibody against Gli349 removes the gliding
Mycoplasmas
from glass but also reduces the gliding speed. As the maximum
(stall) force is 1,800 times larger than that required to pull a
Mycoplasma
cell with the observed gliding speed (see Section 6.3.13), a decrease in the
number of working legs by antibody alone cannot explain the decrease in the
gliding speed. Thus, a drag force caused by the antibody must be considered,
possibly derived from the loosely bound state, i.e., the initial binding state
(f). Removal of a cell by this antibody occurs via a reversal of step (v).
Figure 6.14.
Centipede model for gliding mechanism. The
Mycoplasma
cell mem-
brane is presented by a gray line. Four gliding proteins are assembled around the
cell membrane to form a unit of gliding machinery. The leg protein, Gli349, repeats
the sequence of binding, movement, and release with sialic acid on the solid surface,
and then pulls the cell body forward.
We have estimated that the gliding unit consists of around 450 Gli349
molecules on each cell using the anti-Gli349 antibody [27, 11]. If this is cor-
rect, the units can be expected to cooperate in pulling the cell forward. The
interaction between molecules is enhanced at the micro scale, and the legs are
very flexible. Hence, the movements are likely to cooperate physically. So far,
we have isolated three inhibitory antibodies, and identified mutation points
