A. Subtil et al., Secretion of predicted Inc proteins of Chlamydia pneumoniae by a heterologous type III machinery, MOL MICROB, 39(3), 2001, pp. 792-800
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.