Biomedical Engineering Reference
In-Depth Information
in water, atomic force microscopy (AFM) was applied (see Figure 6.10D). The
molecules on mica showed a morphology in which a large globule about 25nm
in diameter is connected to a smaller one with a filament. Because the images
obtained from AFM generally reflect the stiffness of the molecular parts, the
images suggested that the connecting filament is very flexible. We assigned
the parts of the schematic molecular shape found by the shape and dimension
data of EM, to the images found by AFM.
Detailed analyses of the amino acid sequence were carried out with the
sequence of a plausible ortholog of
M. pulmonis
, MYPU2110 [52]. Gli349 and
MYPU2110 were found to contain, respectively, 18 and 22 repeats of about 100
amino acid residues each (see Figure 6.10C). No sequence homologous to any
of the repeats was found and no compatible fold structure was found among
known protein structures, suggesting that the repeat in these proteins is novel
and takes a new folding structure. Proteolytic analyses of Gli349 revealed that
cleavage positions are often located between the repeats, implying that the
regions connecting the repeats are unstructured, flexible, and exposed to the
environment [52].
The information about the Gli349 molecule is summarized in Figure 6.10C
[53, 52, 27]. The short rod end is suggested to be the N-terminus, where a
transmembrane segment is predicted. Two shorter rods should lie near the cell
membrane, and the longer flexible rod sticks out from the membrane when the
molecule is bonded to a solid surface. This part may lie along the cell surface
when the molecule is not bound to the solid surface. The foot is composed of
the domain near the C-terminus domain and is responsible for binding to the
solid surfaces. We isolated two monoclonal antibodies, each of which removes
gliding
Mycoplasmas
from the solid surface. Both of them bind to the positions
near the flexible hinge marked
theta
2
in Figure 6.10C, suggesting that these
domains perform conformational changes. A mutant strain containing Gli349
with a substitution from serine to leucine at the 2770th amino acid cannot
bind to solid surfaces, and consequently cannot glide, suggesting that the
structure around this amino acid residue is involved in binding.
6.3.7 Gli521 Protein
Gli521 is coded as an ORF of 4728 amino acids featuring transmembrane
segments at both ends, of which the N-terminus one is processed [48]. This
protein was identified as the target of an inhibitory antibody that removes
gliding
Mycoplasmas
from glass.
When the antibodies against this protein are added to gliding
Mycoplas-
mas
, some
Mycoplasmas
are removed from the glass but some remain. The
remaining ratio increases to near 100% with the concentration of antibodies
used. Therefore, we believe that the role of this protein is the motor or the
gear-transmitting force from the motor to the leg. Identification of ATPase
activity in P42, coded downstream of Gli521 on the genome, suggests that
the role of Gli521 is the transmission of force from the motor to the leg, i.e., a
