CHARACTERIZATION OF CHLAMYDIA PNEUMONIAE CDSD AND ITS ROLE IN THE BASAL BODY OF THE TYPE III SECRETION APPARATUS

Abstract

<p><em>Chlamydia pneumoniae </em>is a Gram-negative, obligate intracellular bacterium which shares its unique biphasic developmental cycle, genus-specific lipopolysaccharide, and complement fixation antigen with the other <em>Chlamydia</em> species. Intracellular bacteria, like <em>Chlamydia</em>, require strategies to invade host cells, evade host detection, commandeer host processes, and absorb nutrients in order to support their developmental cycle and survive. The type III secretion (T3S) system meets these needs by transporting bacterial effector proteins across the bacterial membrane and through the host cell membrane. The T3S system in <em>C. pneumoniae </em>is composed of approximately twenty different proteins, whose encoding genes are dispersed throughout ten operons in the <em>Chlamydia</em> genome. CdsD (<em>Cpn0712</em>), a basal body protein component of the T3S apparatus, is suggested to localize to the inner membrane and anchor other T3S structural components of the inner membrane ring. However, the cytoplasmic N-terminal domain contains two putative forkhead-associated (FHA) domains which may play an additional functional role in cellular signalling. This large hypothetical inner-membrane protein is poorly characterized in <em>C. pneumoniae </em>and the role of the predicted phospho-threonine binding, N-terminal FHA domains has yet to be elucidated. Herein, we provide evidence that CdsD has a high affinity for five cytoplasmic (CdsQ, CdsL, CdsN, PknD and SycH) and one periplasmic (CdsF) T3S-associated proteins. We also provide the first evidence that the phosphorylation of CdsD may permit the phosphorylation-dependent oligomerization or interaction with other phosphorylated components of the T3S apparatus. Future research will clarify the role of phosphate signalling in the T3S virulence mechanism. Ultimately, this may lead to a greater understanding of signalling mechanisms that regulate the secretion of bacterial effectors into host eukaryotic cells.</p>