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].