Final Report Summary - CRYOTRANSLATION (High Resolution cryo-EM Analysis of Ribosome-associated Functions)
The project CRYOTRANSLATION enabled structural studies of membrane protein biogenesis and late phases of translation at near atomic resolution. To that end we could provide structural and mechanistic insights into complexes consisting of the translation machinery and protein-conducting channels such as the Sec complex or YidC, that are caught in the middle of nascent membrane protein insertion. We could show that the Sec complex dynamically adjusts to either translocating a hydrophilic or inserting a hydrophobic membrane proteins via opening of its vertical pore or lateral gate, respectively. We also visualized how in this process the oligosaccharyltransferase (OST) specifically integrates into the ribosome-channel complex to execute N-glycosylation cotranslationally. Moreover, we learned that the alternative membrane protein insertase YidC also undergoes conformational transitions for protein insertion, and that it forms a complex with its newly discovered partner YibN, that plays an additional role in the assembly of membrane protein complexes. We provided the first near atomic structure of a human ribosome and, during the late phases of translation, we visualized how a stop codon is recognized in eukaryotes in order to terminate translation. Subsequent recycling by the ATPase ABCE1 of eukaryotic 80S ribosomes by splitting into 40S and 60S subunits could be mechanistically elucidated, as well as the role of the 40S-bound ABCE1 in post-splitting re-initiation activities.