The plastid translocon component TOC36 exhibits an affinity for the bacterial protein translocation process

The 44-kDa envelope polypeptides are active components of the plastid translocon, but their role in plastid protein import remains elusive. One form from Brassica napus (bnToc36B) was previously observed to exert a significant overall effect on bacterial protein translocation, but the nature of the influence requires further characterization. The experimental strategies employed in this study thus focus specifically on the nature of the bnToc36B-bacterial Sec translocon relationship to gain an understanding of Toc36's function. BnToc36B's presence in bacteria created a number of effects related to the protein transport process that together point to functional interactions with the bacterial Sec translocon. These effects are (1) reduced sensitivity to azide impairment as measured by a higher recovery rate from azide treatment, (2) reduced sensitivity to suboptimal temperatures manifesting as sustained levels of protein synthesis and translocation, (3) sustained levels of growth and beta-lactamase transport in high ampicillin concentrations, and (4) evidence for a physical affinity for the bacterial translocon. A reduction in overall SecA levels and a more stable SecA profile, when subjected to azide treatment, was observed in bnToc36B-containing bacteria. The implications of the bacterial data are discussed.