Abstract
Glycogen has been localized both inside and outside Chlamydia trachomatis organisms. We now report that C. trachomatis glycogen synthase (GlgA) was detected in both chlamydial organism-associated and -free forms. The organism-free GlgA molecules were localized both in the lumen of chlamydial inclusions and in the cytosol of host cells. The cytosolic GlgA displayed a distribution pattern similar to that of a known C. trachomatis-secreted protease, CPAF. The detection of GlgA was specific since the anti-GlgA antibody labeling was only removed by preabsorption with GlgA but not CPAF fusion proteins. GlgA was detectable at 12h and its localization into host cell cytosol only became apparent at 24h after infection. The cytosolic localization of GlgA was conserved among all C. trachomatis serovars. However, the significance of the GlgA secretion into host cell cytoplasm remains unclear since, while expression of chlamydial GlgA in HeLa cells increased glycogen stores, it did not affect a subsequent infection with C. trachomatis. Similar to several other C. trachomatis-secreted proteins, GlgA is immunogenic in women urogenitally infected with C. trachomatis, suggesting that GlgA is expressed and may be secreted into host cell cytosol during C. trachomatis infection in humans. These findings have provided important information for further understanding C. trachomatis pathogenic mechanisms.
Highlights
Urogenital tract infection with Chlamydia trachomatis is a leading cause of sexually transmitted bacterial diseases [1,2,3]
We found that only the endogenous glycogen synthase (GlgA) was detected both inside and outside of chlamydial inclusions when the infected cultures were observed either 24h or 40h after infection (Figure 1A), suggesting that a portion of GlgA is secreted into host cell cytosol
When the anti-GST-GlgA antiserum was carefully titrated (B) and analyzed using confocal microscopy (C), we found that GlgA detected inside chlamydial inclusions displayed two distinct patterns with or without overlapping with chlamydial organisms, suggesting that a portion of GlgA is secreted out of chlamydial organisms into the lumen of chlamydial inclusions prior to accessing to host cell cytosol
Summary
Urogenital tract infection with Chlamydia trachomatis is a leading cause of sexually transmitted bacterial diseases [1,2,3]. The C. trachomatis organisms have evolved the ability to secrete proteins into both the inclusion membranes and host cell cytosol and the secreted proteins have been hypothesized to play important roles in modifying host cellular processes for facilitating chlamydial invasion, intracellular survival/replication and spreading to new cells [5,9,10,11,12,13,14,15,16,17,18,19,20,21,22]. We found that of the 6 glycogen metabolism-related enzymes investigated in the current study, only GlgA was detected outside of chlamydial organisms. The above observations together have provided new information and tool for mapping the molecular basis of C. trachomatis pathogenesis
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