Genus-optimized strategy for the identification of chlamydial type III secretion substrates

Abstract

Among chlamydial virulence factors are the type III secretion (T3S) system and its effectors. T3S effectors target host proteins to benefit the infecting chlamydiae. The assortment of effectors, each with a unique function, varies between species. This variation likely contributes to differences in host specificity and disease severity. A dozen effectors of Chlamydia trachomatis have been identified; however estimates suggest that more exist. A T3S prediction algorithm, SIEVE, along with a Yersinia surrogate secretion system helped to identify a new T3S substrate, CT082, which rather than functioning as an effector associates with the chlamydial envelope after secretion. SIEVE was modified to improve/expand effector predictions to include all sequenced genomes. Additional adjustments were made to the existing surrogate system whereby the N terminus of putative effectors was fused to a known effector lacking its own N terminus and was tested for secretion. Expansion of effector predictions by cSIEVE and modification of the surrogate system have also assisted in identifying a new T3S substrate from Chlamydia psittaci. The expanded predictions along with modifications to improve the surrogate secretion system have enhanced our ability to identify novel species-specific effectors, which upon characterization should provide insight into the unique pathogenic properties of each species.

Expression and Targeting of Secreted Proteins from Chlamydia trachomatis

“…In addition, there are now several in silico predictive tools for the identification of putative secreted effector proteins (23,51,52,78). The pBOMB4 vector permits expression of chlamydial proteins under the control of either constitutive or inducible promoters and allows the detection of tagged bacterial proteins by immunofluorescence, immunoblotting, or biochemically.…”

Simkania negevensis, an insight into the biology and clinical importance of a novel member of the Chlamydiales order

“…S. negevensis encodes a type III secretion system (T3SS) (Collingro et al, 2011). Hsia et al first suggested the existence of a type III secretion system in Chlamydia (Hsia et al, 1997), which was likely present in the Chlamydiales common ancestor given its presence in every genome sequenced so far (Bertelli et al, , 2010Greub et al, 2009;Horn et al, 2004;Hovis et al, 2013;Stephens et al, 1998), as summarized in Table 1. The T3SS appears as a needle inserted in the inner and outer membranes of the bacterium, which protrudes into the cytoplasm of the cell through the inclusion membrane (Pilhofer et al, 2013).…”

Development of aChlamydia suis-specific antibody enzyme-linked immunosorbent assay based on the use of a B-cell epitope of the polymorphic membrane protein C

“…Lack of Chlamydia specificity, resulted in the development of tests detecting antibodies against the recombinant Chlamydia full‐length major outer membrane protein (MOMP) (Hoelzle, Hoelzle, & Wittenbrink, ; Verminnen et al., ). Later on, other surface exposed antigens like outer membrane protein 2 (Omp2), polymorphic membrane proteins (Pmp's) and virulence associated antigens like for instance translocated actin‐recruiting phosphoprotein (Tarp), inclusion membrane proteins (Inc's), Chamydia protease‐like activity factor (CPAF) and secreted inner nuclear membrane‐associated Chlamydia protein (SINC) were explored for use in serology, with varying degrees of success in terms of sensitivity and specificity (Forsbach‐Birk et al., ; Hagemann et al., ; Hovis et al., ; Longbottom et al., ; Mojica et al., ; Rahman et al., ; Zhong, Fan, Ji, Dong, & Huang, ). Development of serological tests for Chlamydiae of veterinary interest now focuses towards the use of species‐specific peptides of surface exposed antigens or of virulence associated antigens as it proved to be successful for C. trachomatis diagnosis in humans, leading to several commercial available ELISA's based on the use of highly immunogenic C. trachomatis species‐specific MOMP peptides (the C. trachomatis ‐IgG‐pELISA plus Medac assay, Medac, Wedel, Germany; the SeroCT‐IgG ELISA, Savyon Diagnostics, Ashdod, Israel; the C. trachoma‐ tis IgG EIA Ani Labsystems, Vantaa, Finland).…”