Biomedical Engineering Reference
In-Depth Information
(MPN309), P30 (MPN453), and HMW3 (MPN452) [13, 98, 49, 89, 99].
[45, 74, 13].
Most proteins in these groups except P200 are coded in three loci on the
genome, i.e. i) P1 operon coding P1 adhesin, P90, P40, and one ORF; ii) crl
locus coding P65, HMW2, P41, and P24; and iii) HMW operon coding P30,
HMW3, HMW1 and other 6 ORFs [87]. The proteins in each group are likely
to function at the same time, as often observed for many bacterial systems.
Conversely, the ORFs in these loci could have a role in cytadherence. HMW1,
HMW3, P65, and P200 proteins share a feature in SDS-PAGE, by which they
migrate with much slower speed than that predicted from their molecular
weights. This feature is caused by the obvious bias in amino acid contents,
found in the domains, named “acidic proline rich (APR)”, comprising more
than half of these proteins [88]. This feature in the amino acid sequence may
suggest that these proteins exist in conditions specific for the attachment
organelle, and any difference in the condition from the usual cytosol is reflected
by the translucent appearance of the organelle under EM.
The
M. pneumoniae
genome has the gene for the FtsZ protein, the bacte-
rial tubulin homolog, but not the gene for MreB (the bacterial actin homolog)
both of which are widely distributed in bacteria and function as cytoskeletal
proteins [93, 35]. FtsZ is expressed in
M. pneumoniae
cells [100], but obvious
localization at the attachment organelle was not suggested (our unpublished
data), showing that this protein is not involved in the attachment organelle.
6.4.3 Search for Proteins Involved in Gliding Mechanism, But Not
in Cytadherence
As discussed above, a number of proteins have been identified as being involved
in cytadherence. However, these identifications do not provide direct answers
about the gliding mechanism. Therefore, researchers have decided to isolate
mutants specifically deficient in gliding motility.
Mycoplasmas
were mutated
by transposons, and each clone was examined for spreading of colonies (as
originally done in the studies of
M. mobile
gliding mutants) and also examined
for binding and normal growth rate. Pich et al. used
Mycoplasma genitalium
(closely related to
M. pneumoniae
) and identified two proteins that fit the
criteria [29]. Hasselbring et al. identified 11 proteins of
M. pneumoniae
and
finally focused on three proteins [12]. These results did not immediately resolve
the mystery of gliding, but they did provide some suggestions and tools for
future studies:
i) Mutations in most of the identified proteins did not produce complete
defects in motility. Even when they reduced the motility severely, some
activity remained. The direct involvement of these genes in the gliding
mechanism is unclear, because if they are essential for gliding, some of
transposon-insertion mutants should be defective in gliding. Alternatively,
