Biomedical Engineering Reference
In-Depth Information
Translucent Area (v)
The electron-dense core is surrounded by an electron-lucent area, from which
dense complexes are excluded [73]. Hegermann et al. examined the structure
of this area by treating chemically fixed cells with Triton X-100, and suggested
that spoke structures connect the rod and the cell periphery. Seybert et al.
reported that the proximal end of the rod is attached to the membrane based
on ECT findings. Henderson and Jensen [79], however, proposed that this part
may be filled with fluid having properties distinct from those of cytosol, and
may play a role in transmitting the force and movement generated around the
rod.
6.4.2 Proteins Related to Cytadherence
As cytadherence is a pathogenic determinant, the adhesion protein and ten
other proteins essential for the process have been identified [88, 16, 71]. All
of them examined so far have been localized in the attachment organelle.
Therefore, localization at the attachment organelle is now one of criteria for
identifying cytadherence proteins [13, 49, 89]. The cytadherence-related pro-
teins are also generally essential for gliding, because
Mycoplasmas
can glide
only when they are bound to solid surfaces. Recent progress in the techniques
of genetic rearrangement in
M. pneumoniae
have accelerated identification of
cytadherence proteins [90, 91, 13, 92]. These proteins can be classified into
five groups, based on subcellular localization and roles, as follows (see Figure
6.17)
1
:
i)
P1 adhesin (MPN141):
a 170-kDa protein with transmembrane seg-
ments, responsible for binding to solid surfaces such as host cells, glass,
and plastics provably via sialic acid or sulfated glycolipids [94, 56], and
also for gliding motility [15].
ii)
Proteins that support P1 adhesin with physical interactions:
P90,
P40, (These two proteins are derived from an ORF, MPN142) etc. [95, 96,
49, 89]. These proteins are localized within a rather wide area surrounding
the attachment organelle, like P1 adhesin. The complex formed by P1 and
these proteins may be observed as the nap structure under EM.
iii)
Proteins localizing at the mid part of the rod:
HMW1 (MPN447)
and HMW2 (MPN310). These proteins are essential to the rod formation
[92, 97, 89]. The segmented paired plates of the rod may be composed of
these proteins.
iv)
Proteins localizing at the proximal end of the rod, suggested
to be components of the wheel:
These include P41 (MPN311), P24
(MPN312), and P200 (MPN567)
v)
Proteins localizing near the distal end of the attachment or-
ganelle:
suggested to be components of the terminal button, such as P65
1
ORF names will be noted as well as the conventional protein names [93].
