Molecular basis of Climp63-mediated ER lumen spacing

J Cell Sci. 2023 May 1;136(9):jcs260976. doi: 10.1242/jcs.260976. Epub 2023 Apr 28.


The width of cisternal structures in the endoplasmic reticulum (ER) is maintained by the ER-resident protein Climp63 (also known as CKAP4). Self-association of the Climp63 luminal domain (LD), even though moderate, plays a key role in shaping ER sheets. However, the molecular basis of luminal spacing remains elusive. Here, we analyzed the homotypic interactions of the Climp63 LD using deep learning-predicted structures. The LD is highly α-helical, with a flexible leading helix followed by a five-helix bundle (5HB). Charge-based trans associations were formed between the tip of the 5HB and the C-terminus of the LD, consistent with generating a width of ∼50 nm for ER sheets. The leading helix of the LD was dispensable for homotypic interactions but packing of the 5HB regulated self-association. The density of Climp63, likely reflecting the strength of cis interactions, influenced the ER width, which was maintained by trans interactions. These results indicate that a general principle in maintaining membrane tethering is multi-modular self-association.

Keywords: ER sheet; Luminal width; Membrane tethering; Structural prediction.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Endoplasmic Reticulum* / metabolism