Chlamydia pneumoniae CdsQ functions as a multicargo transport protein, delivering chaperone - effector complexes to the type III secretion ATPase, CdsN

Chlamydia pneumoniae is a Gram-negative, obligate intracellular pathogen thatutilizes a type III secretion system (T3SS) to facilitate invasion of host cells. In C.pneumoniae, CdsN, the T3SS ATPase, has been proposed to facilitate unfoldingof effector proteins by releasing their cognate chaperones. CdsQ is thought tobe the C-ring ortholog of FliN, which interacts with effectors, chaperones, andstructural proteins. We have previously shown that CdsQ interacts with CdsN,however, the role of this interaction is unclear. In this paper, we explored the interactionof CdsQ and CdsN with other T3S components. We identified four novelinteractions between CdsQ and CopN, the YopN plug protein ortholog, Cpn0706,a putative chaperone, Cpn0827, a putative novel effector and LcrH-2, a putativechaperone, all of which have not previously been identified in other T3SS. CdsNhas been shown previously to interact with CopN and Cpn0706 and we reporttwo novel interactions between CdsN and Cpn0827 and LcrH-2. Our findings thatCdsQ binds multiple effectors (Cpn0827 and CopN) and chaperones (LcrH-2 andCpn0706) suggests that CdsQ may act as a multi-cargo transport protein thatshuttles chaperone-effector complexes to the base of the apparatus where CdsQcomplexes may act as a protein scaffold to position chaperone-effector complexesin the context of hexameric CdsN for chaperone release and effector secretion. Wediscuss these new interactions in the context of chaperone-effector delivery andhierarchical secretion of effector proteins in C. pneumoniae.

Author(s):

Raman K. Toor , Chris B. Stone , James B. Mahony

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