Biomedical Engineering Reference
In-Depth Information
part about 4
8nm thick and 8nm wide [81]. This structure is reported to
span the cell membrane with an intracellular domain extending 24nm into
the cytoplasm with a distal wider part. Considering that gliding occurs at the
interface between the cell membrane and a solid surface, this structure may
play the role of the foot, as hypothesized for
M. mobile
.
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Segmented Paired Plates (ii)
In sectional images of the attachment organelle, the center has an electron-
dense core surrounded by a translucent area [82, 84, 85, 73]. After extraction
with Triton X-100 or Triton X-114, an Triton-insoluble shell, which appears to
be a cytoskeletal structure, remains [76, 77, 80]. It is composed of a relatively
thick “rod” and a filamentous network forming a basket-like structure. It was
thought that the rod, i.e., the electron-dense core in sectional images, supports
the attachment organelle and that the basket supports the remainder of the
cell [5, 71]. As the basket cannot be found after treatment of the Triton-
insoluble shell by DNase and RNase (our unpublished data), this structure
may be partly or thoroughly composed of nucleic acids. The isolated rods are
apparently divided into two parts; one is a striated rod and the other is the
distal end structure (terminal button). A recent study using ECT revealed
that this striated rod is actually composed of thicker and thinner segmented
plates paired with about a 7nm gap [79, 81]. The rods are flexible, and are
often bent about 150
◦
just proximal to the midpoints.
Terminal Button (iii)
The distal end of the electron-dense core in the sectional images is enlarged
and attached to the cell membrane; this end is called the “terminal button”
[86, 87, 16, 71, 73]. These features can also be observed in the negatively
stained image of isolated rods, although they are sometimes attached with
membrane pieces, suggesting a complex structure including the polar cell
membrane [78, 80]. ECT studies clarified that the terminal button can be
divided into three major parts; the distal part is attached to the inner layer
of peripheral membrane proteins [79, 81].
Wheel Complex (iv)
Hegermann et al. suggested a striking model, based on the observations of
cryosections by EM [78]. In that model, the rod is attached at its proximal end
to a “wheel complex” with fibrils, which connect the rod and the periphery of
the cell. A similar structure, called the “bowl”, has been found at the proximal
end of rod by ECT, although the fibrils are not easily seen.
