Coordination of translation and assembly of protein complexes
Final Report Abstract
In project P8, we have performed proof of concept experiments demonstrating that protein synthesis and the assembly of oligomeric complexes is frequently coupled. Our studies on bacterial luciferase assembly motivated a broader analysis of protein complex formation in bacteria, demonstrating the prevalence of the process. Extending the original operon concept provided by Jacob and Monod, we further demonstrate that operons, by mediating nearby synthesis, enhance the efficiency of complex assembly. Motivated by these findings, an ongoing collaboration with the group of Reinhard Lipowsky (P9) develops a stochastic model describing how nearby synthesis of complex subunits impacts co- and posttranslational assembly of complexes. So far unpublished work demonstrates the prevalence of cotranslational assembly in bacteria. Revealing the importance of co-translational folding on assembly, SeRP, limited proteolysis and single-molecule measurements show that fully synthesized TrpE engages nascent TrpD only after it has acquired a compacted, near native fold. Another important achievement of our research project was the determination of the nascent interactome of the E. coli SRP, providing the first proteome-wide view on the principles governing SRP-mediated targeting. Ongoing studies demonstrate that SRP recruitment as well as the recruitment of TF and DnaK to translating ribosomes is governed by the intrinsic features of nascent chains and not by a coordinated change of ribosome translation kinetics (Tippmann et al. in preparation). Motivated by our findings on co-translational assembly in bacteria in the context of this consortium, we started new projects in the lab, aiming to assess the coupling of protein complex formation and protein synthesis also in eukaryotes, initially using S. cerevisiae as the model. This led to the discovery, that this mechanism is preserved and prevalent also in eukaryotic cells. Unpublished data furthermore demonstrate that the synthesis of co-translationally assembling yeast complex subunits is spatially constrained, mediated by co-localized mRNAs. Finally, recent studies of protein complex assembly in mammalian U2OS and HEK293 cells imply the existence of yet another translation-coupled mechanism to assemble homo-oligomeric complexes, which is based on the interaction of two nascent polypeptides, that are most likely synthesized in the context of a polysome by ribosomes translating the same mRNA.
Publications
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Operon structure and cotranslational subunit association direct protein assembly in bacteria, Science. 350, 678-80 (2015)
Shieh, Y. W., Minguez, P., Bork, P., Auburger, J. J., Guilbride, D. L., Kramer, G. & Bukau, B.
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Global profiling of SRP interaction with nascent polypeptides, Nature. 536, 219-23 (2016)
Schibich, D., Gloge, F., Pohner, I., Bjorkholm, P., Wade, R. C., von Heijne, G., Bukau, B. & Kramer, G.
