Endoplasmic Reticulum Structure Determines Optimal Ribosome Density

TL;DR

This paper presents a biophysical model explaining how the structure of the endoplasmic reticulum influences ribosome density, predicting structural preferences based on protein demand and comparing results with experimental data.

Contribution

The study introduces a model linking ER structure to ribosome distribution, providing a physical explanation for structural differences and their functional implications.

Findings

Flat sheets require higher ribosome coverage to match flux

Tubules need fewer ribosomes due to higher capture efficiency

Model predictions align with experimental observations

Abstract

Recent work has shown an increasing interest in understanding the structure of the endoplasmic reticulum (ER) and how ribosomes are displayed on it. Here we present a model that explains a physical reason for why the cell creates different structures of the ER. Due to the diffusion of biomolecules, we find that flat sheets and a matrix of tubules have different regimes of optimized capture efficiency. We extend the model to explain the observed difference in density of ribosomes on the structures of the ER. Due to the capture efficiency of tubules, less ribosomes are needed on those structures. For flat sheets, more ribosome coverage at biological separation distance is needed to match the same fraction of relative flux. We then push the model to predict that depending on the future life of the translated protein and overall demand for protein expression, the cell will utilize one structure of the ER over another. Predictions are compared with experimental data.