The Tic40 translocon components exhibit preferential interactions with different forms of the Oee1 plastid protein precursor.

The transport of proteins across the plastid envelope involves a host of proteinaceous components that attend to varying structural needs of the process. This study focuses on interactions between two select forms (designated Tic40 and Toc36) of the Tic40-related components and different structural versions of the Oee1 precursor to dissect the components' mode of operation. Interaction profiling revealed several features pertaining to how Tic40-related components might work during the transport process. The main operational features revealed are: (1) Tic40 interacts preferentially with Oee1 precursors containing only the plastid-targeting domain, (2) Toc36 interacts preferentially with Oee1 precursors containing both plastid- and thylakoid lumen-targeting domains, (3)carboxyl truncations to either the entire Oee1 precursor or Toc36 affect interactions negatively, and (4) the general reduction of Tic40-related protein levels in transgenic plants appears to exert a greater negative impact on endogenous Oee1 levels than the other proteins assessed, a trend that corroborates the findings of the protein interaction experiments.