Exploiting Antigenic Diversity for Vaccine Design THE CHLAMYDIA ArtJ PARADIGM

Wepresent an interdisciplinary approach that, by incorporating a range
of experimental and computational techniques, allows the identification
and characterization of functional/ immunogenic domains. This approach
has been applied to ArtJ, an arginine-binding protein whose orthologs in
Chlamydiae trachomatis (CT ArtJ) and pneumoniae (CPn ArtJ) are shown to
have different immunogenic properties despite a high sequence similarity
(60\% identity). We have solved the crystallographic structures of CT
ArtJ and CPn ArtJ, which are found to display a type II transporter fold
organized in two alpha-beta domains with the arginine-binding region at
their interface. Although ArtJ is considered to belong to the periplasm,
we found that both domains contain regions exposed on the bacterial
surface. Moreover, we show that recombinant ArtJ binds to epithelial
cells in vitro, suggesting a role for ArtJ in host-cell adhesion during
Chlamydia infection. Experimental epitope mapping and computational
analysis of physicochemical determinants of antibody recognition
revealed that immunogenic epitopes reside mainly in the terminal (D1)
domain of both CPn and CT ArtJ, whereas the surface properties of the
respective binding-prone regions appear sufficiently different to assume
divergent immunogenic behavior. Neutralization assays revealed that sera
raised against CPn ArtJ D1 partially reduce both CPn and CT infectivity
in vitro, suggesting that functional antibodies directed against this
domain may potentially impair chlamydial infectivity. These findings
suggest that the approach presented here, combining functional and
structure-based analyses of evolutionary-related antigens can be a
valuable tool for the identification of cross-species immunogenic
epitopes for vaccine development.