INTRODUCTION:
Francisella tularensis is a Gram-negative coccobacillus [1]
that is the causative agent of tularemia (rabbit fever), a disease that
results in extreme respiratory illness and distress that can be fatal
without treatment [2]. Tularemia can be spread through bug bites or
contracted through an airborne route. It was considered a viable
biological weapon and its actual use in WWII was claimed, even though
this claim was later disputed [3]. Despite extensive research onF. tularensis , we still do not fully understand its virulence
mechanisms, and the functions of many of its proteins are unknown.
However, F. tularensis studies on mouse infection models
identified several proteins that were highly upregulated during
infection and strongly reacted with the mouse immune system. [4].
While most of these proteins have a known role in F. tularensispathogenicity, one of the standouts was an uncharacterized protein
encoded by a gene in the locus FTT_1539. In another study in which mice
were infected with F. tularensis type A strain FSC033 [5],
the amounts of bacterial proteins isolated from infected mice were
compared to that in bacteria that were cultured in vitro and it
was found that the abundance of FTT_1539 increased by more than 4-fold
[6, 7]. The protein FTT_1539 was also shown to co-purify with the
membrane fraction and to be recognized by antibodies as playing a role
in cell surface associations [8]. All these observations support the
hypothesis that FTT_1539 may play a role in F. tularensisvirulence, or more generally, in its interactions with the host. In
addition, FTT_1539 is identified as an immunodominant antigen, which
suggests its possible use as a tularemia vaccine candidate [9].
To further our understanding of the possible role of the FTT_1539
protein as the F. tularensis virulence factor, its structure was
determined by the Center for Structural Genomics of Infectious Diseases
(CSGID) and its coordinates were deposited to the Protein Data Bank
(PDB) with the code 4QVR. In this paper we describe the structure and
provide genomic analyses of FTT_1539.