Mutual stabilization of the XcpZ and XcpY components of the secretory apparatus in Pseudomonas aeruginosa

Protein secretion in Gram-negative bacteria is often dependent on the gener al secretory pathway (GSP). In Pseodomonas aeruginosa, this system requires at least 12 Xcp (Gsp) proteins, which are proposed to constitute a multipr otein complex localized in the bacterial envelope. Hitherto, little was kno wn about the mutual interactions between Xcp proteins. In this study, mutan ts affected in the xcpZ gene encoding a bitopic inner-membrane protein were analysed to investigate the role of this protein in the architecture of th e secretory machinery. The absence of XcpZ resulted in a decreased amount o f XcpY. Reciprocally, XcpZ was not detectable in a xcpY mutant, demonstrati ng a mutual stabilization of these two proteins. These results strongly sug gest that XcpZ and XcpY interact within the functional secretory apparatus.