Analyses of the dynamic interplay between ribosomes and bacterial translocon complexes

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The interaction of membrane-embedded translocon complexes with translating ribosomes is a crucial prerequisite for protein sorting in both eu- and prokaryotic organisms. Although the translational activity of the ribosome is sufficient for integrating some bacterial membrane proteins into the lipid phase, many others require the ATPase SecA in addition. How SecA is able to access a nascent chain while the ribosome stays attached to the SecYEG translocon is currently unknown. Our goal is to determine the dynamic interaction of ribosomes and SecA in actively transporting SecYEG translocons by site-directed cross-linking and by dissecting the different stages of transport using reconstitution assays. The universally conserved YidC functions as a bacterial integration site, both in concert with SecYEG but also independently of SecYEG. There are conflicting data on how proteins are targeted to YidC and whether this is a strict co-translational process involving the bacterial SRP pathway. It is also unknown, how YidC interacts with SecYEG during co-translational integration and whether SecYEGdependent and –independent substrates are handled differently by YidC. We want to address these questions by combining in vivo techniques like site-directed in vivo cross-linking and FRET with in vitro techniques, like in vitro transport assays using reconstituted proteoliposomes and affinity measurements.