title: Interactions between CdsD, CdsQ, and CdsL, three putative Chlamydophila pneumoniae type III secretion proteins.
abstract: Chlamydophila pneumoniae is a gram-negative obligate intracellular bacterial pathogen that causes pneumonia and bronchitis and may contribute to atherosclerosis. The developmental cycle of C. pneumoniae includes a morphological transition from an infectious extracellular elementary body (EB) to a noninfectious intracellular reticulate body (RB) that divides by binary fission. The C. pneumoniae genome encodes a type III secretion (T3S) apparatus that may be used to infect eukaryotic cells and to evade the host immune response. In the present study, Cpn0712 (CdsD), Cpn0704 (CdsQ), and Cpn0826 (CdsL), three C. pneumoniae genes encoding yersiniae T3S YscD, YscQ, and YscL homologs, respectively, were cloned and expressed as histidine- and glutathione S-transferase (GST)-tagged proteins in Escherichia coli. Purified recombinant proteins were used to raise hyper-immune polyclonal antiserum and were used in GST pull-down and copurification assays to identify protein-protein interactions. CdsD was detected in both EB and RB lysates by Western blot analyses, and immunofluorescent staining demonstrated the presence of CdsD within inclusions. Triton X-114 solubilization and phase separation of chlamydial EB proteins indicated that CdsD partitions with cytoplasmic proteins, suggesting it is not an integral membrane protein. GST pull-down assays indicated that recombinant CdsD interacts with CdsQ and CdsL, and copurification assays with chlamydial lysates confirmed that native CdsD interacts with CdsQ and CdsL. To the best of our knowledge, this is the first report demonstrating interactions between YscD, YscQ, and YscL homologs of bacterial T3S systems. These novel protein interactions may play important roles in the assembly or function of the chlamydial T3S apparatus.
authors.affiliation: M. G. DeGroote Institute for Infectious Disease Research, Faculty of Health Sciences and the Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Dustin L
authors.initials: DL
authors.lastname: Johnson
authors.forename: Chris B
authors.initials: CB
authors.lastname: Stone
authors.forename: James B
authors.initials: JB
authors.lastname: Mahony
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D016993:Chlamydophila pneumoniae / Q000235:genetics / Q000502:physiology*; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D002479:Inclusion Bodies / Q000737:chemistry; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins