To confirm this observation we utilized formaldehyde fixation followed by PAGE analysis to visualize the formation of dimers. Using this method we saw that Cpn0859 migrated in two molecular forms, with sizes corresponding to both monomers and dimers. We then explored possible interactions between Cpn0859 and the other flagellar proteins and detected

interactions of Cpn0859 with both FliI and FlhA, but not FliF. Cpn0859 bound to the N-terminal 150 amino acids of FliI and the cytoplasmic region of FlhA. The interaction of Cpn0859 with the cytoplasmic domain of FlhA was expected MK5108 price as FlhA is known to interact with soluble components of other flagellar see more systems [34]. We considered the possibility that Cpn0859 may in fact be the FliH ortholog in C. pneumoniae as Cpn0859 has minor sequence orthology to other FliH proteins, but after further investigation we found that Cpn0859 did not appear to play a regulatory role with FliI (data not shown). Figure 6 summarizes the interactions between FliI, FlhA and FliF (Figure 6A) and interactions between Cpn0859, FlhA and FliI (Figure 6B). Figure 6 Interacting regions between FliI and FlhA, FliF, and Cpn0859. A: FliF contains two transmembrane regions and interacts with the cytosolic domain of FlhA by its extreme C-terminal end. FlhA contains

seven transmembrane regions and interacts with the N-terminal

region of FliI by its cytoplasmic domain. FliI contains a Walker A and B domain and mediates protein interactions by its N-terminus. B: Cpn0859 appears to dimerize, and interacts with the cytosolic domain of FlhA and the N-terminal 150 amino acids of FliI. Bacterial type III secretion (T3S) and flagellar secretion systems are structurally similar, and may have a Poziotinib mouse common ancestry [21]. Although C. pneumoniae does not contain a full repertoire of flagellar genes, it does encode a complete T3S system which most likely consists of specific protein complexes located in the inner membrane [16, 20, 23]. We have characterized an interaction of FliI with CdsL, the T3S ATPase tethering protein. The C. pneumoniae FliH ortholog has not yet been identified, and in the absence of FliH, CdsL may play a Selleck Bortezomib regulatory role for both FliI and CdsN. FliI also interacts with the CopN, the T3S plug protein, suggesting that FliI may be involved in either the secretion of effector proteins or regulation of the T3S system. YscU orthologs have a flagellar paralog, FlhB, and Cpn0322 is believed to be the C. pneumoniae YscU ortholog (CdsU). FlhB is known to interact with FlhA, but in C. pneumoniae no FlhB ortholog has been annotated. We found that FlhA interacts with CdsU, suggesting integration of FlhA into the inner membrane, associating with T3S components.