The obligate intracellular bacterial pathogen, Chlamydia trachomatis, is the leading cause of sexually transmitted infections. Due to its obligate intracellular life, it has been difficult to unravel the molecular mechanisms involved in its biphasic developmental cycle and the establishment of the intracellular inclusion in which multiplication of chlamydiae is taking place. Using ultra high pressure liquid chromatography and tandem mass spectrometry of trypsin-cleaved proteins from whole cell lysates of C. trachomatis L2 infected HeLa cells; we determined and quantified the protein content. We unambiguously identified a total of 57,147 HeLa cell peptides, representing 5956 proteins, and 3807 chlamydial peptides representing 526 proteins, or 59% of the open reading frames in C. trachomatis L2 genome.
We also searched for known secreted inclusion membrane proteins (Inc). A total of 19 Inc proteins were identified and 14 of these could be quantified having an altered expression level when samples from 20 and 43 hours post infection were compared. IncG, CT288, CT223, IncE, CT147 and CT728 were the most up-regulated Inc proteins illustrating the usefulness of this method. Furthermore, CT642 and CT846 were detected.