Key result
Cryo-EM reveals ribosome-channel complexes maintain similar structures featuring a lateral opening regardless of translocating polypeptides.
No direct clinical translation for membrane protein disorders; leaves open dynamic gating roles of lateral openings in vivo.
Cotranslational translocation of proteins requires ribosome binding to the Sec61p channel at the endoplasmic reticulum (ER) membrane. We have used electron cryomicroscopy to determine the structures of ribosome-channel complexes in the absence or presence of translocating polypeptide chains. Surprisingly, the structures are similar and contain 3-4 connections between the ribosome and channel that leave a lateral opening into the cytosol. Therefore, the ribosome-channel junction may allow the direct transfer of polypeptides into the channel and provide a path for the egress of some nascent chains into the cytosol. Moreover, complexes solubilized from mammalian ER membranes contain an additional membrane protein that has a large, lumenal protrusion and is intercalated into the wall of the Sec61p channel. Thus, the native channel contains a component that is not essential for translocation.
No takes yet. Share an insight, caveat, or question.
Ménétret et al. (2000) studied this question. Electron cryomicroscopy of ribosome-channel complexes was evaluated on Structure of ribosome-channel complexes in the absence or presence of translocating polypeptide chains. Electron cryomicroscopy revealed that ribosome-channel complexes have similar structures with or without translocating polypeptides, containing 3-4 connections that leave a lateral opening.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context:
More from Molecular Cell