A trapped translocating intermediate (left) fits two hydrophilic segments (gray lines) within a single translocon pore. Upon releasing the trap (green), translocation proceeds normally (right).
Proteins are inserted into the ER in eukaryotes and the plasma membrane in prokaryotes by the Sec61-based translocon. Data from several studies, including crystal structures, indicate that the translocon's pore consists of a single Sec61α subunit, thus creating a narrow channel. But the new studies suggest the pore is much larger than expected.
The authors trapped intermediates in the translocation process by adding a streptavidin-binding peptide tag to the NH2-terminal end of the inserted protein. When streptavidin was added, translocation stalled, resulting...
