Conformational transition of Sec machinery inferred from bacterial SecYE structures

Abstract

Over 30% of proteins are secreted across or integrated into membranes. Their newly synthesized forms contain either cleavable signal sequences or non-cleavable membrane anchor sequences, which direct them to the evolutionarily conserved Sec translocon (SecYEG in prokaryotes and Sec61, comprising α-, γ-and β-subunits, in eukaryotes). The translocon then functions as a proteinconducting channel 1 . These processes of protein localization occur either at or after translation. In bacteria, the SecA ATPase 2,3 drives post-translational translocation. The only high-resolution structure of a translocon available so far is that for SecYEβ from the archaeon Methanococcus jannaschii 4 , which lacks SecA. Here we present the 3.2-Å-resolution crystal structure of the SecYE translocon from a SecA-containing organism, Thermus thermophilus. The structure, solved as a complex with an anti-SecY Fab fragment, revealed a 'pre-open' state of SecYE, in which several transmembrane helices are shifted, as compared to the previous SecYEβ structure 4 , to create a hydrophobic crack open to the cytoplasm. Fab and SecA bind to a common site at the tip of the

Conformational Dynamics of the Plug Domain of the SecYEG Protein-conducting Channel

“…This structure supports the idea that membrane segments can be inserted before the plug has vacated its central position (15). The crystal structure of the Thermus thermophilus SecYE with a bound anti-SecY Fab fragment shows only a partial opening of the lateral gate at the cytoplasmic side, also termed the hydrophobic crack (16). Also here, the plug domain remains at its central position.…”

Assembly of outer-membrane proteins in bacteria and mitochondria

“…the LPS deacylase LpxR from Salmonella typhimurium (PDB file 3FID) (Rutten et al, 2009), and of a typical a-helical inner-membrane protein, i.e. the SecYE translocon of Thermus thermophilus (PDB file 2ZQP) (Tsukazaki et al, 2008), are shown on the left and the right, respectively.…”

MifM Monitors Total YidC Activities of Bacillus subtilis, Including That of YidC2, the Target of Regulation

“…In bacteria, the SecYEG membrane protein complex provides pathways of protein translocation across and integration into the cytoplasmic membrane (1)(2)(3). The crystal structures of SecYEG reveal an hourglass-shaped pore across the membrane, which is plugged with a short helix in the resting state (4)(5)(6). As a substrate comes in, either by SecA-mediated translocation or signal recognition particle (SRP)-mediated cotranslational targeting, the plug is displaced, and the channel with the open gate accepts the translocating chain (7)(8)(9).…”

“…SecA translocates not only secretory proteins but also large extracytoplasmic regions of integral membrane proteins (10). For lipid phase integration, a transmembrane region of the substrate exits the pore laterally through the lateral gate that opens toward the lipid phase of the bilayer (4)(5)(6). This process is thought to be driven by the thermodynamic partition of the hydrophobic segment to the lipidic environment (11).…”