Secretion of predicted Inc proteins of Chlamydia pneumoniae by a heterologous type III machinery

Chlamydia spp, are strictly intracellular pathogens that grow inside a vacu ole, called an inclusion. They possess genes encoding proteins homologous t o components of type ill secretion machineries, which, in other bacterial p athogens, are involved in delivery of bacterial proteins within or through the membrane of eukaryotic host cells. Inc proteins are chlamydial proteins that are associated with the inclusion membrane and are characterized by t he presence of a large hydrophobic domain in their amino acid sequence. To investigate whether Inc proteins and other proteins exhibiting a similar hy dropathic profile might be secreted by a type iii system, we used a heterol ogous secretion system. Chimeras were constructed by fusing the N-terminal part of these proteins with a reporter, the Cya protein of Bordetella pertu ssis, and these were expressed in various strains of Shigella flexneri. We demonstrate that these hybrid proteins are secreted by the type III secreti on system of S. flexneri, thereby providing evidence that Inca, IncB and In cC are secreted by a type ill mechanism in chlamydiae. Moreover, we show th at three other proteins from Chlamydia pneumoniae, ail of which have in com mon the presence of a large hydrophobic domain, are also secreted by S, fle xneri type ill secretion machinery.