2025-10-29 マックス・プランク研究所
Structure of the ribosome-bound SND3 translocon complex from the heat-tolerant fungus Chaetomium thermophilum. The SND3 translocon inserts proteins into the endoplasmic reticulum membrane as they are produced by the ribosome.© Louise Duever
<関連情報>
- https://www.mpg.de/25599408/snding-proteins-into-the-membrane
- https://www.nature.com/articles/s41467-025-65357-z
SND3は、SEC61トランスロコン複合体内の膜挿入酵素です SND3 is the membrane insertase within a distinct SEC61 translocon complex
Tzu-Jing Yang,Saumyak Mukherjee,Julian D. Langer,Gerhard Hummer & Melanie A. McDowell
Nature Communications Published:29 October 2025
DOI:https://doi.org/10.1038/s41467-025-65357-z
Abstract
During the biogenesis of most eukaryotic integral membrane proteins (IMPs), transmembrane domains are inserted into the endoplasmic reticulum membrane by a dedicated insertase or the SEC61 translocon. The SRP-independent (SND) pathway is the least understood route into the membrane, despite catering for a broad range of IMP types. Here, we show that Chaetomium thermophilum SND3 is a membrane insertase with an atypical fold. We further present a cryo-electron microscopy structure of a ribosome-associated SND3 translocon complex involved in co-translational IMP insertion. The structure reveals that the SND3 translocon additionally comprises the complete SEC61 translocon, CCDC47 and TRAPɑ. Here, the SEC61β N-terminus works together with CCDC47 to prevent substrate access to the translocon. Instead, molecular dynamics simulations show that SND3 disrupts the lipid bilayer to promote IMP insertion via its membrane-embedded hydrophilic groove. Structural and sequence comparisons indicate that the SND3 translocon is a distinct multipass translocon in fungi, euglenozoan parasites and other eukaryotic taxa.
