title: The chlamydial periplasmic stress response serine protease cHtrA is secreted into host cell cytosol.
abstract: BACKGROUND
  The periplasmic High Temperature Requirement protein A (HtrA) plays important roles in bacterial protein folding and stress responses. However, the role of chlamydial HtrA (cHtrA) in chlamydial pathogenesis is not clear.
  
  
  RESULTS
  The cHtrA was detected both inside and outside the chlamydial inclusions. The detection was specific since both polyclonal and monoclonal anti-cHtrA antibodies revealed similar intracellular labeling patterns that were only removed by absorption with cHtrA but not control fusion proteins. In a Western blot assay, the anti-cHtrA antibodies detected the endogenous cHtrA in Chlamydia-infected cells without cross-reacting with any other chlamydial or host cell antigens. Fractionation of the infected cells revealed cHtrA in the host cell cytosol fraction. The periplasmic cHtrA protein appeared to be actively secreted into host cell cytosol since no other chlamydial periplasmic proteins were detected in the host cell cytoplasm. Most chlamydial species secreted cHtrA into host cell cytosol and the secretion was not inhibitable by a type III secretion inhibitor.
  
  
  CONCLUSIONS
  Since it is hypothesized that chlamydial organisms possess a proteolysis strategy to manipulate host cell signaling pathways, secretion of the serine protease cHtrA into host cell cytosol suggests that the periplasmic cHtrA may also play an important role in chlamydial interactions with host cells.
authors.affiliation: Department of Microbiology and Immunology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA.
authors.forename: Xiang
authors.initials: X
authors.lastname: Wu
authors.forename: Lei
authors.initials: L
authors.lastname: Lei
authors.forename: Siqi
authors.initials: S
authors.lastname: Gong
authors.forename: Ding
authors.initials: D
authors.lastname: Chen
authors.forename: Rhonda
authors.initials: R
authors.lastname: Flores
authors.forename: Guangming
authors.initials: G
authors.lastname: Zhong
mesh_terms: D015153:Blotting, Western; D002458:Cell Fractionation; D002692:Chlamydia trachomatis / Q000201:enzymology* / Q000472:pathogenicity*; D003600:Cytosol / Q000737:chemistry*; D019085:Fluorescent Antibody Technique, Direct; D006367:HeLa Cells; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D033903:Periplasmic Proteins / Q000378:metabolism*; D021381:Protein Transport; D057057:Serine Proteases / Q000378:metabolism*; D037521:Virulence Factors / Q000378:metabolism*
chemical_list: D006360:Heat-Shock Proteins; D033903:Periplasmic Proteins; D037521:Virulence Factors; D057057:Serine Proteases