Basic HTML Version
Journal of Mosquito Research, 2013, Vol.3, No.4, 21
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32
ISSN 1927-646X
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30
it smaller than the vertebrate transferrin (Yoshiga et al.,
1997). Up-regulation of the transferrin transcript upon
infection with entomopathogenic nematodes-bacteria
was proved to be an appropriate response. A vertebrate
type of transferrin with two iron-binding sites would
be a more effective antibiotic agent than mosquito
transferrin with its single iron-binding site. It has been
hypothesized that the N-terminal lobe allows
transferrin to sequester iron from the invading parasite,
and the absence of C-terminal lobe may be a
mechanism to prevent iron sequestering by the
invading parasite from the host insect (Cornelissen
and Sparling, 1994). This mechanism could deprive
the parasite of its iron requirements. However, some
bacteria that are pathogenic to vertebrates have
acquired transferrin receptors that allow them to
acquire iron from transferrin in a process termed
“iron-piracy” (Schryvers and Gonzalez, 1990). These
receptors interact principally with the C-terminal lobe
only (Alcantara et al., 1993; Retzer et al., 1996). The
insect transferrins may have evolved to modify the
C-terminal lobe to prevent its binding to the receptors
elaborated by the pathogens to escape from the piracy
action of the pathogen (Yoshiga et al., 1997). The
transferrin is found constitutively and was found to be
upregulated upon infection. This molecule can be
suggested to function as both iron sequestering and
iron transport protein (Kontoghiorghes and Weinberg,
1995). As the structure and iron binding capacity of
Dipteran insects and human are different, members of
the transferrin superfamily may serve the same
function in insects that their homologues do in
vertebrates. In the case of the flesh fly (Kurama et al.,
1995), have suggested that transferrin is a vitellogenic
protein that is taken up by developing oocytes. As the
transferrin is present constitutively, it may be involved
in iron transport. Vertebrate transferrin receptors show
high affinity for diferric transferrin, and less for
monoferric or apotransferrin. Therefore, if transferrin
is to be used by insects to transport iron to cells, the
insect receptor must have sufficient affinity for a
monoferric form to operate effectively (Yoshiga et al.,
1997).
The results obtained indicate that, when the purified
recombinant Tsf protein of approximate molecular
mass of 63 KDa was tested against the Mach1™- T1
®
E. coli
strain, it was found that this
E. coli
strain was
sensitive to
Cx. quinquefasciatus
Tsf protein as a clear
inhibition zone appeared (Figure 9). This result
indicated that the recombinant protein is a potent
inhibitor for the growth of the Mach1™- T1
®
E. coli
strain. Isolation of a cDNA clone encoding an
A.
aegypti
transferrin, when treated with heat-killed
bacterial cells, mosquito cells in culture respond by
up-regulating several protein (Kurama et al., 1995).
Among these is a 66-KDa protein. A recombinant Tsf
protein was generated using pET system from
A.
aegypti
and
A. albopictus
. Also, a recombinant Tsf
protein of the same size was purified using pET
system in BL21 bacterial cells, the expression of Tsf
in
Cx. quinquefasciatus
upon infection with the filarial
parasite,
Wuchereria bancrofti.
was detected
(Beerntsen et al., 2000).
A. aegypti
defensin is
expressed at very high concentration in an individual
mosquito (Lowenberger et al., 1999). Meanwhile, in
A.
gambiae
, this antibacterial peptide is expressed at
much lower levels but has more antibacterial activity
than
A. aegypti
defensing (Richman et al., 1996).
However, the discrepancy between the model
relationship and that explored is not simply explained
by immune-responsiveness of the mosquito. This
explanation does not take into account the significant
contribution of the parasite to the mosquito-parasite
relationship. The phylogeny of the Trfs closely
follows the dipteran phylogeny, clustering
Cx.
quinquefasciatus
with
A. aegypti
and
An. gambiae
of
the suborder Nematocera and clustering the three
dipterans
D. melanogaster
,
G. m. morsitans
, and
S.
peregrina
of the suborder Brachycera, forming a
well-supported branch with the Nematocera. Also,
clustering
Cx. quinquefasciatus
with
A. aegypti
of the
subfamily Culicinae while separating
A. gambiae
representing subfamily Anophilinae. Within the
Brachyceran dipteran cluster, the two members of the
Calyptrata section of the
S. peregrina
and
G. m.
morsitans
are grouped separately from
D.
melanogaster
, which is a member of the Acalyptrata
section. This division refers to the development of the
calypteres (small lobe at the base of the wing), which
are well developed in the Calyptrate section (Odronitz