Biomedical Engineering Reference
In-Depth Information
affecting gliding and binding [42, 47, 48, 27, 28]. Mapping of working points
of these effectors on the gliding proteins has shown that the effectors are well
explained by this working model.
This model has been suggested based on observations of
M. mobile
. Ob-
viously, this model can be applied to
Mycoplasma
species closely related to
M. mobile
, such as
M. pulmonis
, whose genomes contain easily detectable or-
thologs of gliding proteins. But what about nonrelated species, such as those
belonging to the
pneumoniae
group? Because of the poor gliding activity, it
has not been easy to conduct such extensive analyses on other gliding
My-
coplasmas
, but recently we obtained similar results for
M. pneumoniae
gliding
using an anti-P1 antibody [48]. The antibody reduced the gliding speed of
M.
pneumoniae
and eventually removed the cells from the glass surface. This
suggests that the mechanism of
Mycoplasma
gliding may be universal.
6.3.15 Toward a Complete Model
Although we can explain all of our current observations with the mechani-
cal cycle described in Section 6.3.14, the model has not been substantiated
adequately and the details remain to be clarified. We recently identified a
jellyfish-like cytoskeletal structure inside the head and neck. Although it is
suggested to interact with gliding proteins we do not know the role of this
jellyfish structure in the mechanism. Does it support the gliding machinery
mechanically? Does it sort the gliding proteins? Does it have more direct roles
in the movement? To obtain a more concrete understanding, we need more
information about the following issues: i) whole and atomic images of ma-
chinery, ii) detection and analysis of actual movements of the machinery by
fluorescent labeling and force measurement, iii) mathematic inspection of a
working model, and iv) reconstruction of the motility system.
6.3.16 Origin of Gliding Mechanism
Because no other proteins as yet have been found to be related to gliding
proteins, we cannot know the origins of the gliding mechanism. Generally,
Mycoplasmas
, which parasitize animal tissues, have advanced systems for anti-
genic variations. Mvsps are suggested to be involved in the antigenic varia-
tions, as discussed in Section 6.3.4 [6, 42]. MvspI (the largest Mvsp at 220 kDa)
is an abundant surface protein clustering at regions other than the neck. We
isolated this protein, and characterized and observed it using EM with rotary
shadowing. The protein forms a homodimer, where the C-terminal flexible
filamentous parts stick out from the N-terminal globular part. The outline of
this protein is reminiscent of the whole shape of the gliding unit as presented
by Figure 6.15 [53]. The amino acid sequences of Mvsps also feature repeats
of about 90 amino acids, although the sequence is not common with those
of Gli349. These observations may suggest that the gliding proteins and the
antigenic proteins may share an ancestor protein.
