CONCLUSION/DISCUSSION:
The analysis presented here highlights the presence of a common
structural motif in a large group of diverse secreted proteins from a
broad range of human pathogens such as Franciscella tularensis ,Helicobacter pylori and Mycobacterium tuberculosis . Although the
sequence identity between these proteins is low, their overall structure
contains the signature SHS2 motif and they all are secreted or located
on the bacterial cell surface during infection and were broadly
classified as virulence factors. Interestingly, most of these proteins
also form homodimers. This suggest that the tandem duplication in
FTT_1539 could be important for its function, mimicking the dimer
arrangement of other proteins from this clan. Of these proteins only
3VNC has been functionally and structurally characterized and the
location of matched regions in the structures of the FTT_1539 and the
homologs discussed here suggests a possible similarity in their function
and pathogenicity.
The genome of F. tularensis contains components homologous to
Type I, IV and VI secretion systems [24], suggesting a mechanism for
how the FTT_1539 protein can be secreted. Analogies with the function
of Tip-α and connecting fragmentary knowledge of the functions of other
proteins from this group allows us to propose that FTT_1539 may be
involved in interactions with the host inflammatory pathways, and the
suppression of the inflammatory immune response activation through
intracellular molecules such as TNF-α [24].